Physical 
Sci.Llb. 

IN 

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no.  6 

1974 


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J«C»li«   Llll^^ihii^l 


LIBRAK'k 

UNIVERSITY  OF  CALIFORIJU 

DAVIS 


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CAIvlKORNIA  STATE  MINING  BURKAXJ. 

J.  J.  CRAWFORD,  State  Mineralogists^ 


Bulletin  no.  6.         San  Francisco,  September,  1895. 


CALIFORNIA 


GOLD  MILL  PRACTICES. 


By  ED.  B.  PRESTON,  M.E,, 

Field  Assistant. 


SACRAMENTO: 
A.  J.  JOHNSTON,   :::::::  superintendent  state  printing. 

1901. 

^"^H-^-r IT- ^-  — ^' «•* 


DAVIS 


CALIKORNIA    STATE     IVIINING    BURKAU. 

J.   J.   CRAWFORD,   State   Mineralogist. 


BULLETix   NO.  6.  San  Francisco,  September,  1895. 


CALIFORNI.^ 


GOLD  MILL  PRACTICES. 


Bv  ED.  B.  PRESTOX.  M.E., 


Field  As.sistant. 


SACRAMENTO: 
A.  J.  JOHNSTON,     ::::::     superintendent  .state  printing. 

1895. 


Hon.  J.  J.  Crawford,  State  Mineralogist: 

In  preparing,  at  your  request,  this  article  on  the  California  Gold  Mill 
Practices,  I  have  endeavored  to  furnish  something  that  should  be  of 
practical  benefit  to  actual  working  millmen  who  might  not  come  in 
reach  of  expensive  works  on  the  subject,  rather  than  a  further  contri- 
bution to  the  literature  on  gold  milling.  A  demand  for  this  kind  of  a 
work  is  evidenced  by  the  constant  inquiry  at  the  State  Mining  Bureau 
for  former  Reports  dealing  in  part  on  this  subject. 

To  W.  H.  Storms,  M.E.,  my  acknowledgments  for  valuable  data 
collected  in  the  counties  of  Amador,  Calaveras,  Tuolumne,  and  Mari- 
posa are  due. 

Some  of  the  illustrations  are  repeated  from  former  Bureau  publica- 
tions, and  for  many  of  the  others  I  am  indebted  to  the  principal  San 
Francisco  iron  works,  including  the  Union,  Risdon,  Hendy,  Fulton,  and 

the  Pelton  Company. 

ED.  B.  PRESTON,  M.E., 

Field  Assistant. 

San  Francisco,  Cal.,  January,  1895. 


NOTES  ON  GOLD  MILLING  IN  CALIFORNIA. 


The  system  of  reduction  of  gold-bearing  ores  with  stamps,  as  at  pres- 
ent carried  out  in  California,  is  the  result  of  progressive  improvement 
during  the  past  forty-four  years.  The  first  successful  mill  in  this  State 
was  built  in  the  winter  of  1850-51,  and  used  steam  for  power. 

Starting  with  the  ancient  Mexican  arrastra,  crushing,  with  the  help 
of  a  mule  and  one  man,  a  few  hundred  pounds  of  ore  at  a  charge,  we 
have  progressed  to  the  present  aggregation  of  mechanical  appliances, 
as  seen  in  the  modern  stamp-mill,  requiring  great  motive  power,  and 
disposing  of  hundreds  of  tons  of  ore  in  the  course  of  a  day.  This  pro- 
gression is  largely  the  result  of  accumulated  practical  experience  on  the 
part  of  the  designers  and  builders  of  mills,  as  well  as  of  the  millmen 
in  the  handling  of  the  various  gold  ores.  Of  late  years  scientific  inves- 
tigations have  greatly  aided  in  improving  both  the  process  and  the 
mechanism. 

That  the  results  accomplished  have  been  of  economic  value  is  evident 
from  the  fact  that  while  formerly  a  yield  of  30%  to  40%  of  the  total 
gold  in  the  ore  was  the  average  obtained,  the  best  mills  of  to-day  are 
able  to  more  than  double  these  figures.  That  our  methods  may  still  be 
improved  upon,  and  the  margin  of  wasted  gold  be  further  narrowed 
down,  is  the  point  for  which  all  intelligent  millmen  are  striving.  While 
the  stamp-mill  itself  had  been  used  for  crushing  ores  long  before  the 
discovery  of  gold  in  California,  since  that  time  it  has  been  greatly 
improved  in  detail,  and  its  capacity  and  eflSciency  increased,  hence 
what  is  now  known  as  the  "  California  gold  mill "  is  a  very  different 
aftair  from  the  clumsy  mills  first  used  for  crushing  quartz  in  this  State. 
The  California  gold-milling  processes  and  the  California  millmen  are, 
as  a  result,  finding  due  recognition  outside  of  their  own  immediate  field 
of  operation,  as  is  evidenced  by  the  increasing  outside  and  foreign  de- 
mand for  our  men  and  milling  machinery.  The  development  of  the 
milling  process,  keeping  pace  with  the  improvement  of  the  machinery 
required  for  ore  reduction,  has  had  the  beneficial  effect  of  greatly  lessen- 
ing the  working  expenses,  permitting  ores  of  a  low  grade  to  be  worked 
at  a  profit.  California  has  a  great  abundance  of  this  class  of  ores,  com- 
paratively untouched,  and  these  must  be  mainly  relied  on  in  the  future 
as  the  sources  of  the  precious  metal.  Already,  under  extremely  favorable 
conditions,  ores  are  being  mined  and  milled  in  California  at  a  cost  of  50 
cents  per  ton,  as  at  the  Spanish  Mine,  in  Nevada  County,  where,  with 
Huntington  roller  mills,  ores  yielding  85  cents  per  ton  have  been  worked 
at  a  profit. 

MILL    SITE. 

When  assured  of  a  constant  and  sufficient  supply  of  ore,  it  is  of  the 
greatest  importance  that  the  site  for  the  mill  should  be  chosen  with  due 
regard  for  economic  treatment.  This  necessitates  the  observance  of  the 
following  points:  The  means  of  transportation  of  the  ore  from  the  mine 


5  CALIFOKNIA   GOLD    MILL   PRACTICES. 

to  the  mill,  which  should  be  done  automatically,  or  at  least  with  as 
little  handling  as  possible,  conveying  the  ore  at  once  to  the  highest 
point  in  the  mill,  so  that  it  will  descend  by  gravity  from  one  to  the 
other  in  all  the  different  consecutive  operations.  Another  important 
feature  is  to  provide  sufticient  space  for  capacious  ore-bins,  which  are 
necessary  to  prevent  a  stoppage  of  the  mill  through  a  lack  of  ore, 
caused  through  unavoidable  delays  in  the  mine  or  along  the  roads. 
The  accessibility  of  the  mill  site  as  regards  fuel,  water,  or  electrical 
transmission,  according  to  the  motive  power  to  be  used,  and  their  con- 
tinuity and  cost  at  all  seasons  of  the  year,  must  likewise  be  considered. 
The  possibility  of  placing  the  levels  for  the  different  floors  on  solid  rock 
foundations  should  be  investigated,  as  stability  of  the  machinery  is 
most  essential  for  successful  milling. 

The  ideal  site  would  be  to  have  the  mill  in  close  proximity  to,  but 
below  the  level  of,  the  collar  of  the  shaft  or  the  mouth  of  the  tunnel, 
on  sloping  ground,  where  the  ore  can  be  delivered  directly  from  the 
mine  to  a  "  grizzly  "  on  the  upper  floor  of  the  mill,  to  be  passed  later, 
without  rehandling,  through  the  crushers,  ore-bins,  self-feeders,  mortars, 
etc.,  while  leaving  sufficient  space  for  a  waste  dump.  For  a  mill  arranged 
in  this  manner,  including  concentrators  and  canvas  platforms,  40'  of 
fall  should  be  available.  If  chlorination  works  are  also  to  be  used,  a 
greater  fall  is  desirable. 

MILL    CONSTRUCTION. 

After  deciding  on  a  suitable  site,  the  surface  should  be  removed  down 
to  the  bedrock  and  leveled  off  for  the  different  floors.  Solidity  and 
accessibility  are  the  chief  points  to  be  observed  in  placing  the  different 
parts  of  the  mill.  Where  required,  heavy  stone  walls  should  be  erected 
as  buttresses.  The  foundation  for  the  mortars  and  the  proper  erection 
of  the  battery  frames  are  points  requiring  particular  attention.  For 
the  mortar-block,  a  trench  is  prepared  of  suitable  depth,  preferably  in 
solid  bedrock,  proportioned  to  the  height  of  the  block,  and  wide  enough 
to  leave  about  2'  of  free  space  around  it,  which  is  later  filled  in  with 
concrete  or  tailings  from  the  battery.  These  mortar-blocks  vary  from 
8'  to  15'  in  length  and  are  dressed  at  the  upper  end  to  the  size  of  the 
bed-plate  of  the  mortar.  In  California  they  can  be  obtained  frequently 
from  a  solid  cut  of  a  pine  tree,  or  else  consist  of  two  or  three  sawed 
blocks  fitted  and  bolted  together  ;  but  where  clear  timber  of  the  requi- 
site size  is  difficult  to  obtain,  the  block  can  be  constructed  of  2"  plank, 
as  is  done  in  the  Black  Hills  in  Dakota.*  There  the  bottom  of  the 
trench  for  the  block  is  leveled  and  some  sand  tamped  down,  on  which 
two  layers  of  2"  plank  are  placed  crosswise  and  spiked  to  each  other, 
and  made  perfectly  horizontal.  On  this  foundation  a  mortar-block  is 
constructed  of  2"  planks,  from  11'  to  14'  long,  according  to  the  depth  of 
the  trench.  The  planks,  which  should  be  of  clear  lumber,  and  varying 
breadths  (in  order  to  break  joints),  stand  on  end,  with  their  width 
parallel  to  the  long  side  of  the  mortar.  They  are  spiked  together  and 
fastened  above  and  below  with  binders  bolted  to  each  other  by  trans- 
verse rods  ;  the  upper  binders  (8"x  12")  being  even  with  the  top  of  the 
mortar-blocks;  the  lower  binders  (r2"xl2")  are  3'  lower. 

The  top  of  the  mortar-block  should  be  planed  perfectly  true  and 

*Gold  Milling  in  the  Black  Hills,  bv  H.  O.  Hoffman.    Transactions  of  the  American 
Institute  of  Mining  Engineers,  Vol.  17,' 1888-89. 


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CALIFORNIA    GOLD    MILL    PRACTICES.  V 

leveled,  and  where  several  blocks  are  placed  in  line  all  the  blocks  should 
be  sawed  otf  to  one  height.  Before  setting  the  mortar  upon  the  block 
a  sheet  of  rubber  cloth,  i"  thick,  should  be  placed  between,  or  when  this 
is  not  obtainable,  two  or  three  folds  of  mill  blankets,  well  tarred,  will 
answer  the  purpose. 

The  mudsills  should  be  of  square  timber,  free  from  sap,  bedded  in  con- 
crete on  the  bedrock  and  secured  by  anchor  bolts  to  the  foundation; 
they  also  should  be  bolted  to  the  linesills. 

The  uprights  of  the  battery  frames  are  supported  in  various  styles: 
with  diagonal  braces  and  hog  chains  at  front  or  back,  or  with  so-called 
knee-frames.  In  the  former  style  the  brace  is  placed  on  the  same  side 
as  the  counter-shaft,  which  rests  low  down  on  the  battery-sills.  This 
style  is  well  suited  for  small  mills  using  stam|:)S  not  to  exceed  750  lbs., 
but  for  large  mills  using  heavy  stamps  the  knee-frames  are  the  more 
suitable,  with  the  counter-shaft  on  a  level  with  the  cam-shaft.  What 
is  known  as  the  reversed  knee-frame  forms  a  strong,  compact  construc- 
tion, but  requires  the  counter-shaft  to  rest  on  the  battery-sills  behind 
the  frame.  The  accompanying  cuts  show  the  construction  of  back  and 
front  knee-braces  as  supplied  with  mills  from  the  Union  Iron  Works  of 
San  Francisco. 

Fig.  2  presents  a  view  of  a  back-knee  battery  frame  with  a  Union 
mortar  and  square  ore-bins,  showing  the  latest  arrangement  of  working 
the  self-feeder  from  a  collar  on  the  stem,  instead  of  having  the  tappet 
strike  the  bumper. 

Fig.  3  shows  the  back-knee  battery  frame  with  the  cams  revolving 
toward  the  ore-bin,  with  a  Hayward  mortar. 

Fig.  4  shows  the  suspended  ore-feeder  with  back-knee  frame. 

Fig.  5  is  the  arrangement  of  a  front-knee  battery  frame,  with  Union 
mortar. 

Figs.  6  and  7  show  the  method  of  securing  knees  to  the  battery  posts. 

The  battery  posts  are  made  24"  deep,  and  from  12"  to  20"  wide;  the 
center  one  of  a  ten-stamp  mill  being  made  the  heaviest,  as  having  to 
bear  the  greatest  strain.  They  are  let  into  the  sills  and  secured  to  the 
line  timbers  by  bolts.  Besides  the  braces,  the  posts  are  given  stability 
above  the  mortar  by  the  guide-timbers  (see  Fig.  6),  which  extend  from 
end  to  end  in  one  piece,  and  are  let  into  the  posts  to  which  they  are 
bolted.  The  lower  one  is  placed  about  6"  above  tlie  upper  edge  of  the 
mortar,  and  the  center  of  the  upper  one  is  about  3'  from  the  top  of  the 
post.  The  seat  for  the  cam-shaft  bearings  is  cut  in  the  upper  part  of 
the  posts. 

After  lowering  the  mortar  on  the  block,  with  the  planed  bottom  rest- 
ing evenly  on  the  sheet  of  rubber  cloth  or  folds  of  tarred  blanket,  it  is 
fastened  perfectly  rigid  by  eight  bolts,  four  on  each  long  side,  passing 
through  the  flange,  which  is  cast  on  the  bottom  of  the  mortar.  This 
flange  is  4"  wide  and  about  2V'  thick.  The  feed  floor  should  be  high 
enough  so  that  these  bolts  can  be  conveniently  reached,  to  permit  their 
tightening  when  required.  The  journals  for  the  cam-shaft,  which  are 
placed  in  the  recesses  cut  out  of  the  battery  posts  for  their  recej)tion, 
are  lined  up  and  "babbitted"  prior  to  receiving  the  cam-shaft  with  its 
cams.  The  stems  are  placed  from  i"  to  1"  from  the  cam-shaft,  and  just 
far  enough  from  the  cams  to  clear  them  when  dropping.  The  cam-shaft 
is  made  of  wrought  iron  or  soft  steel,  from  4V'  to  5"  in  diameter,  turned 
true,  and  should  have  key-seats  for  securing  the  cams.     There  should 


CALIFORNIA    GOLD    MILL    PRACTICES.  \) 

leveled,  and  where  several  blocks  are  placed  in  line  all  the  blocks  should 
be  sawed  otF  to  one  height.  Before  setting  the  mortar  upon  the  block 
a  sheet  of  rubber  cloth,  i"  thick,  should  be  placed  between,  or  when  this 
is  not  obtainable,  two  or  three  folds  of  mill  blankets,  well  tarred,  will 
answer  the  purpose. 

The  mudsills  should  be  of  square  timber,  free  from  sap,  bedded  in  con- 
crete on  the  bedrock  and  secured  by  anchor  bolts  to  the  foundation; 
they  also  should  be  bolted  to  the  linesills. 

The  uprights  of  the  battery  frames  are  supported  in  various  styles: 
with  diagonal  braces  and  hog  chains  at  front  or  back,  or  with  so-called 
knee-frames.  In  the  former  style  the  brace  is  placed  on  the  same  side 
as  the  counter-shaft,  which  rests  low  down  on  the  battery-sills.  This 
style  is  well  suited  for  small  mills  using  stamf)S  not  to  exceed  750  lbs., 
but  for  large  mills  using  heavy  stamps  the  knee-frames  are  the  more 
suitable,  with  the  counter-shaft  on  a  level  with,  the  cam-shaft.  What 
is  known  as  the  reversed  knee-frame  forms  a  strong,  compact  construc- 
tion, but  requires  the  counter-shaft  to  rest  on  the  battery-sills  behind 
the  frame.  The  accompanying  cuts  show  the  construction  of  back  and 
front  knee-braces  as  supplied  with  mills  from  the  Union  Iron  Works  of 
San  Francisco. 

Fig.  2  presents  a  view  of  a  back-knee  battery  frame  with  a  Union 
mortar  and  square  ore-bins,  showing  the  latest  arrangement  of  working 
the  self-feeder  from  a  collar  on  the  stem,  instead  of  having  the  tappet 
strike  the  bumper. 

Fig.  3  shows  the  back-knee  battery  frame  wdth  the  cams  revolving 
toward  the  ore-bin,  with  a  Hayward  mortar. 

Fig.  4  shows  the  suspended  ore-feeder  with  back-knee  frame. 

Fig.  5  is  the  arrangement  of  a  front-knee  battery  frame,  with  Union 
mortar. 

Figs.  6  and  7  show  the  method  of  securing  knees  to  the  battery  posts. 

The  battery  posts  are  made  24"  deep,  and  from  12"  to  20"  wide;  the 
center  one  of  a  ten-stamp  mill  being  made  the  heaviest,  as  having  to 
bear  the  greatest  strain.  They  are  let  into  the  sills  and  secured  to  the 
line  timbers  by  bolts.  Besides  the  braces,  the  posts  are  given  stability 
above  the  mortar  by  the  guide-timbers  (see  Fig.  6),  which  extend  from 
end  to  end  in  one  piece,  and  are  let  into  the  posts  to  which  they  are 
bolted.  The  lower  one  is  placed  about  6"  above  tlie  upper  edge  of  the 
mortar,  and  the  center  of  the  upper  one  is  about  3'  from  the  top  of  the 
post.  The  seat  for  the  cam-shaft  bearings  is  cut  in  the  upper  part  of 
the  posts. 

After  lowering  the  mortar  on  the  block,  with  the  planed  bottom  rest- 
ing evenly  on  the  sheet  of  rubber  cloth  or  folds  of  tarred  blanket,  it  is 
fastened  perfectly  rigid  by  eight  bolts,  four  on  each  long  side,  passing 
through  the  flange,  which  is  cast  on  the  bottom  of  the  mortar.  This 
flange  is  4"  wide  and  about  2^"  thick.  The  feed  floor  should  be  high 
enough  so  that  these  bolts  can  be  conveniently  reached,  to  permit  their 
tightening  when  required.  The  journals  for  the  cam-shaft,  which  are 
placed  in  the  recesses  cut  out  of  the  battery  posts  for  their  recej^tion, 
are  lined  up  and  "babbitted"  prior  to  receiving  the  cam-ehaft  with  its 
cams.  The  stems  are  placed  from  i"  to  1"  from  the  cam-shaft,  and  just 
far  enough  from  the  cams  to  clear  them  when  dropping.  The  cam-shaft 
is  made  of  wrought  iron  or  soft  steel,  from  4i"  to  5"  in  diameter,  turned 
true,  and  should  have  key-seats  for  securing  the  cams.     There  should 


10 


CALIFORNIA   GOLD    MILL    PRACTICES. 


Fig.  6.    Method  of  Securing  Knees  to  Battery  Posts. 

be  two  key-seats,  and  placed  one  third  of  the  shaft  circumference  apart. 
At  one  end  of  the  cam-shaft  the  cast-iron  "hub"  of  the  belt  pulley 
(with  flanges)  is  keyed  on.  This  pulley  is  built  of  wood,  and  turned 
true  on  the  shaft.  Where  there  is  more  than  one  battery  to  the  mill,  it 
is  best  to  have  a  cam-shaft  for  each  ten  stamps,  as  this  permits  of  repairs, 
such  as  changing  cams,  etc.,  without  stopping  more  than  ten  stamps. 

The  guides  (see  Figs.  6  and  7,  and  D,  E,  and  F  of  Fig.  8),  which 
direct  the  drop  of  the  stems,  are  in  two  sets,  upper  and  lower — the 
former  above  the  tappets,  and  the  latter  below  the  cams — and  are 
bolted  to  the  guide-girts  by  eight  bolts.  They  are  best  made  of  hard 
wood,  but  pine  answers  sufficiently  well — though  the  former  lasts  five 
times  as  long  as  pine.  The  old  style  guide  (F,  of  Fig.  8)  consists  of 
two  pieces  of  4"  plank  14"  wide,  planed  on  all  sides,  and  of  sufficient 
length  to  fit  easily  between  the  battery  posts,  with  equi-distant  semi- 
circular grooves,  fitting  together,  for  the  passage  of  the  stems.  A  quick 
and  exact  way  to  make  these  grooves  is  to  clamp  the  two  planed  planks 
tightly  together  as  they  are  to  be  placed  on  the  frame,  set  them  on  edge, 
and,  after  marking  off  the  centers  for  the  five  stems,  bore  out  the  circle 


CALIFORNIA    GOLD    MILL    PRACTICES. 


11 


Fig.  7.    Method  of  Securing  Kxees  to  Batteky  Posts. 


(using  the  joint  line  for  the  point  of  center)  with  a  long-handled  auger 
having  an  adjustable  bit.  These  are  kept  in  many  mills  for  this  special 
purpose. 

Before  bolting  the  guides  in  place,  half-inch  pieces  are  placed  between 
the  two  halves,  and  adjoining  each  stem,  which  are  planed  down  later 
as  the  guides  wear,  leaving  but  little  play  for  the  stem.  After  boring 
out  the  grooves  for  the  stems,  and  before  putting  the  guides  in  place, 
they  should  be  lubricated.  A  convenient  and  economical  plan  is  to  cut 
some  semi-circular  pieces  of  thin  sheet  iron  of  a  somewhat  larger 
diameter  than  the  grooves,  and  drive  them  into  the  wood  at  both  ends 
of  the  channel ;  then  lay  the  halves  level,  groove  side  up,  and  fill  the 
latter  with  linseed  oil,  letting  them  remain  until  the  wood  has  taken 
up  all  it  will  absorb,  when  the  remainder  is  returned  to  the  can,  and 
the  sheet-iron  pieces  removed. 

If,  in  a  pine  guide,  those  portions  occupied  by  the  grooves  are  cut 
out  square,  and  hard-wood  bushings  fitted  in  before  boring  out,  the 
stem  will  work  parallel  to  the  wood  fiber,  which  reduces  the  friction, 


12 


CALIFORNIA   GOLD    MILL    PRACTICES. 


CALIFORNIA    GOLD    MILL    PRACTICES. 


13 


and  lengthens  the  life  of  the  guides;  while  only  the  hard- wood  bushings 
would  need  replacing,  making  the  cost  of  the  guides  less. 

The  great  drawback  to  these  guides  is  that  when  a  stem  has  to  be 
removed,  the  entire  battery  has  to  stop;  hence  the  adoption  of  separate 
guides  for  each  stem,  being  either  all  iron  (see  D,  Fig.  8),  or  wooden 
bushing  in  iron  frames  (see  E,  Fig.  8),  which  are  held  in  place  by 
wedges  and  the  lips  of  the  iron  frames. 

For  the  support  of  the  stamp-stems  when  suspended,  wooden  latch- 
fingers,  or  jacks,  are  supplied.     (See  Figs.  6  and  7,  and  L,  of  Fig.  8.) 


Fig.  9.    Ovekhead  Traveling  Crabs. 

A  jack-shaft,  3"  in  diameter,  rests  in  bearings  attached  to  the  inner 
sides  of  the  battery  posts;  on  this,  cup-shaped  sockets  ride,  in  which 
the  wooden  fingers  are  attached,  shod  at  the  upper  end  with  an  iron 
plate  -J"  thick,  and  provided  with  an  iron  or  leather  "hand-hold  "  near 
the  top. 

For  the  greater  convenience  of  quickly  removing  and  replacing  stems, 
or  cam-shafts,  large  mills  are  supplied  with  overhead  travelers,  or 
''crabs,"  in  line  with  the  batteries,  in  connection  with  a  chain  block 
and  tackle  running  on  plates  secured  to  the  roof,  shod  with  iron  track- 
ing. To  easily  reach  the  cams,  tappets,  etc.,  a  platform  is  placed  just 
below  the  cam-shaft. 

The  feed-floor  consists  of  a  double  board  floor  of  1"  lumber,  with 
broken  joints,  supported  on  joists  18"  apart,  and  about  2'  below  the  feed 
opening  in  the  mortar. 

MILL    DETAILS. 


The  Grizzly  is  a  coarse  screen  consisting  of  a  number  of  parallel  bars 
attached  to  a  frame,  set  on  an  angle  from  45°  to  55°,  over  the  ore-bin. 
These  bars  may  be  of  round,  rectangular,  or  V-shaped  (apex  down) 
iron,  or  of  wood,  faced  with  iron,  and  resting  on  several  iron  cross-rods, 
held  apart  with  iron  washers;  the  distance  between  the  bars  should  be 
equal  to  the  opening  the  rock-crusher  jaws  are  set  to — from  2"  to  3". 
There  are  no  fixed  dimensions  of  length  or  breadth,  as  these  depend  in 
a  measure  on  local  conditions;  but  they  are  usually  from  3'  to  6'  wide, 
and  long  enough  (12'  to  15')  to  give  the  fine  material  time  to  drop 
through  the  spaces  before  reaching  the  crusher  floor. 

Where  substantial  steel  T  rails  are  used  for  tracking  in  the  mine,  they 
can  be  made  to  serve  for  grizzly-bars  when  no  longer  of  use  in  tlie  mine, 
by  turning  them  with  the  base  up. 


14 


CALIFORNIA   GOLD    MILL    PRACTICES. 


The  grizzly  should  be  placed  at  the  highest  point  of  the  mill  over  the 
ore-bin,  where  the  car  or  wagon  can  enter  and  dump.  Its  chief  object  is 
to  separate  at  once  the  finely  divided  ore  from  the  coarser;  a  secondary 
purpose  is  served  in  affording  an  opportunity  to  recover  drills,  gads,  or 
hammers  that  may  have  come  from  the  mine,  in  the  ore,  before  they  reach 
the  rock-breaker  or  mortar.  Its  lower  end  rests  on  a  platform  in  front 
of  the  rock-crusher,  or  better,  in  a  chute  with  an  adjustable  end-gate 
placed  above  the  mouth  of  the  rock-crusher  so  as  to  permit  of  its  being 
fed  automatically. 

Where  the  ore  as  delivered  from  the  mine  carries  less  than  5%  of  fine 
stuff,  the  grizzly  should  be  dispensed  with,  especially  where,  in  con- 


FiG.  10.    Gkizzlies. 


structing  the  mill,  fall  must  be  economized.  Some  object  to  the  use  of 
the  grizzly,  as  tending  to  feed  all  the  hard  rock  by  itself,  and  say  the 
output  of  those  batteries  is  below  the  others. 

Rock-Breahers  or  Crushers  are  placed  on  a  platform  below  the  grizzly 
and  above  the  ore-bin  in  such  a  manner  that  the  crushed  rock  mingles 
with  the  fine  stuff  passing  between  the  bars  of  the  grizzly.  The  rock- 
breaker  must  be  of  sufficient  weight  to  remain  firm  in  its  place,  and 
strong  enough  to  resist  heavy  strains;  the  dies  should  be  easy  to 
exchange  and  adjust,  and  all  parts  requiring  to  be  oiled  should  be 
arranged  to  prevent  oil  coming  in  contact  with  the  quartz.  In  large 
mills  it  is  best  to  have  one  crusher  to  supply  everv  twenty  stamps,  and 
on  account  of  their  intermittent  work,  they  should  have  driving  power 
separate  from  that  of  the  stamps. 

Rock-breakers  are  adjusted  to  crush  the  rock  smaller  than  the  throat 
of  the  mortar  (therefore,  less  than  3"),  but  as  the  work  of  the  rock- 
breaker  is  cheaper  than  that  of  the  stamp,  it  would  jDay,  with  very  hard 
rock,  to  do  more  of  the  crushing  with  this  machine,  even  to  the  extent 
of  placing  two  crushers,  one  beneath  the  other,  and  bringing  the  quartz 
greatly  reduced  to  the  stamps. 

There  are  two  general  types  of    rock-crushers.     The  older  pattern 


Fig.  11.    Rock-Dreaker,  Clakk  Patteun. 


i'lkj.   ii.      K  .^K-1'1  H.kL,h     hLikh,   P\TTERN, 


FUi.   12.      IloCK-r.REAKER,    UlAKK   I'ATTEKN, 


CALIFORNIA    GOLD    MILL    PRACTICES. 


15 


carries  a  flat,  fixed  jaw,  working  with  one  having  a  reciprocating  motion 
and  using  flat  or  corrugated  dies  that  are  reversible.  The  Blake  is  rep- 
resentative of  this  pattern.  The  other  pattern  has  an  outer,  circular, 
fixed  jaw,  within  which  a  corrugated  jaw  circles,  of  which  the  Gates  is 
representative.  This  latter  machine  permits  of  larger  blocks  being  fed. 
It  is  an  excellent  machine  for  heavy  work,  and  where  the  rock  is  not  wet 
or  clayey;  but  it  requires  greater  horse-power,  for  where  a  Blake,  10"  by 
8",  crushing  3  tons  per  hour,  requires  9  H.  P.,  the  Gates,  with  a  diameter 
of  37-i",  crushing  3^  tons  per  hour,  requires  16  H.  P.  The  Gates  con- 
sists of  a  nearly  vertical  shaft  of  forged  steel,  rotated  from  below  by  a 


Fig.  U.    Ore-Bi>-  Gate. 

beveled  wheel  set  V'  out  of  center,  on  the  top  of  which  a  chilled-iron 
conical  head  is  attached,  with  the  base  downward,  rotating  within 
chilled-iron  concaves,  with  an  outward  slope,  set  in  the  cylindrical  body 
of  the  machine.  Between  these  two  faces  the  ore  is  crushed,  their  dis- 
tance apart  below  being  gauged  by  set-screws.  The  shaft,  by  being 
made  to  revolve  around  an  eccentric  at  the  bottom,  has  a  constant  crush- 
ing power  without  doing  any  grinding.  A  set  of  concaves  lasts  two 
years,  and  can  be  replaced;  the  center  shaft  with  the  chilled-iron  head 
has  been  known  to  crush  120,000  tons  of  an  average  hard  quartz  before 
wearing  out. 

Ore-bins  should  always  be  as  spacious  as  the  surroundings  will  per- 
mit, but  never  of  less  capacity  than  will  carry  a  twenty-four  hours  supply 
for  the  mill,  say  about  65  cu.  ft.  to  the  stamp.  They  are  usualh'  con- 
structed with  a  sloping  bottom,  to  facilitate  discharging,  but  where 
very  large  bins  can  be  erected  this  feature  is  not  so  essential.  These 
bottoms  must  be  solidly  braced  and  ought  to  be  covered  with  iron  plates 
over  those  portions  where  the  ore  has  to  l^e  dropped.  The  front  of  the 
bin  is  parallel  with  the  mortars  and  supplied  with  gates  for  each  battery 
above  the  level  of  the  hopper  of  the  self-feeders.  These  gates  sliould  be 
regulated  by  a  pinion  and  rack,  and  set  for  a  regular  discharge  and 
delivery,  through  chutes,  into  the  self-feeders.  The  chutes  should  be 
lined  with  heavy  sheet  iron. 


/     J 


Fig.  13.    Gates'  Eoce;-Bee.\keb. 


CALIFORNIA    GOLD    MILL    PRACTICES. 


15 


carries  a  flat,  fixed  jaw,  working  with  one  having  a  reciprocating  motion 
and  using  flat  or  corrugated  dies  that  are  reversible.  The  Blake  is  rep- 
resentative of  this  pattern.  The  other  pattern  has  an  outer,  circular, 
fixed  jaw,  within  which  a  corrugated  jaw  circles,  of  which  the  Gates  is 
representative.  This  latter  machine  permits  of  larger  blocks  being  fed. 
It  is  an  excellent  machine  for  heavy  work,  and  where  the  rock  is  not  wet 
or  clayey;  but  it  requires  greater  horse-power,  for  where  a  Blake,  10"  by 
8",  crushing  3  tons  per  hour,  requires  9  H.  P.,  the  Gates,  with  a  diameter 
of  37-i",  crushing  3^  tons  per  hour,  requires  1 6  H.  P.  ,  The  Gates  con- 
sists of  a  nearly  vertical  shaft  of  forged  steel,  rotated  from  below  by  a 


Fig.  14.    Ore-Bin  Gate. 

beveled  wheel  set  -i"  out  of  center,  on  the  top  of  which  a  chilled-iron 
conical  head  is  attached,  with  the  base  downward,  rotating  within 
chilled-iron  concaves,  with  an  outward  slope,  set  in  the  cylindrical  body 
of  the  machine.  Between  these  two  faces  the  ore  is  crushed,  their  dis- 
tance apart  below  being  gauged  by  set-screws.  The  shaft,  by  being 
made  to  revolve  around  an  eccentric  at  the  bottom,  has  a  constant  crush- 
ing power  without  doing  any  grinding.  A  set  of  concaves  lasts  two 
years,  and  can  be  replaced;  the  center  shaft  with  the  chilled-iron  head 
has  been  known  to  crush  120,000  tons  of  an  average  hard  quartz  before 
wearing  out. 

Ore-bins  should  always  be  as  spacious  as  the  surroundings  will  per- 
mit, but  never  of  less  caj^acity  than  will  carry  a  twenty-four  hours  supply 
for  the  mill,  say  about  65  cu.  ft.  to  the  stamp.  They  are  usually  con- 
structed with  a  sloping  bottom,  to  facilitate  discharging,  but  where 
very  large  bins  can  be  erected  this  feature  is  not  so  essential.  These 
bottoms  must  be  solidly  braced  and  ought  to  lie  covered  with  iron  plates 
over  those  portions  where  the  ore  has  to  lie  dropped.  The  front  of  the 
bin  is  parallel  with  the  mortars  and  supplied  with  gates  for  each  battery 
above  the  level  of  the  hopper  of  the  self-feeders.  These  gates  should  l)e 
regulated  by  a  pinion  and  rack,  and  set  for  a  regular  discharge  and 
delivery,  through  chutes,  into  the  self-feeders.  The  chutes  should  be 
lined  with  heavy  sheet  iron. 


16 


CALIFORNIA   GOLD    MILL    PRACTICES. 


Fig.  15.    Hendy  Ch.\llenge  Ure-Feeder. 

Self-Feeders. — The  entire  value  of  the  stamp  battery  hinges  on  a  regu- 
lar and  even  feeding,  and  as  it  can  be  done  much  better  (from  15%  to 
20%)  by  a  machine  than  by  hand,  this  latter  method  has  become  well 
nigh  extinct  in  California.  Among  the  mechanical  feeders  mostly  used 
are  the  Challenge  (in  two  patterns),  TuUoch,  Stanford,  and  Roller 
feeders.  Although  the  three  latter  are  very  serviceable  for  certain  classes 
of  ore,  and  are  cheaper  in  first  cost,  the  Challenge  is  undoubtedly 
the  best  all-round  machine,  which  is  proved  by  its  almost  universal 
adoption.  They  are  either  placed  on  a  frame  which  runs  on  an  iron 
track  in  the  feed  floor,  back  of  and  at  right  angles  to  the  battery,  or  are 
suspended  from  tracks  supported  by  the  battery  posts  and  standards 
placed  against  the  ore-bin.  This  latter  pattern  permits  of  greater 
accessibility  to  the  feed  side  of  the  mortar.  In  general,  the  Challenge 
feeders  consist  of  a  hopper  with  a  movable  circular  plate  beneath,  set 
slightly  inclined  toward  the  mortar,  receiving  a  rotary  motion  by  means 
of  gear  wheels  acting  on  the  lower  face  of  the  plate,  which  are  moved 


CALIFORNIA   GOLD    MILL    PRACTICES. 


17 


Fig.  16.    Tulloch  Automatic  Ore-Feedbr. 

by  a  friction  grip  that  receives  its  impetus  from  a  blow  of  the  descend- 
ing stem  on  a  bumper-rod  connected  with  it.  Movable  wings  extending 
from  the  point  of  the  hopper  over  the  plate  toward  the  throat  of  the 
mortar  permit  a  given  quantity  of  the  ore  to  be  scraped  off  at  each  blow 
through  a  partial  rotation  of  the  plate.  The  older  machines  were  made 
with  right  or  left-handed  bumpers,  but  the  present  and  better  plan  is  to 
place  the  rod  in  the  center,  so  that  the  third  stamp  in  a  five-stamp  bat- 
tery imparts  the  blow.  The  newest  machines  have  no  bumper-rod,  but 
are  worked  by  a  collar  fastened  on  the  stem  above  the  top  of  the  mortar. 
Each  battery  is  supplied  with  its  own  self-feeder. 

The  Tulloch  feeder  consists  of  a  square  frame,  into  which  a  hop- 
per fits,  having  below  a  tray  suspended  from  the  frame  at  any  de- 
sired angle,  and  in  such  a  manner  as  to  have  a  forward  and  backward 
swinging  motion  inside  the  frame,  which  can  be  arrested  on  the  forward 
motion  at  a  certain  point  by  lugs,  underneath  the  tray,  striking  a  bar. 
The  back  of  the  hopper  is  supplied  with  an  adjustable  scraper,  and  at 
each  motion  of  the  tray  a  certain  amount  of  the  ore  is  scraped  forward 
and  falls  into  the  battery.  The  machine  is  operated  by  the  descent  of 
the  stamp. 

Mortars. — The  mortars  in  California  are  mostly  single-discharge,  and 
cast  in  one  piece,  extremely  solid.  When  required  in  places  inaccessible 
by  wagon  roads,  they  are  cast  in  pieces,  which  are  later  bolted  together. 
Their  interior  form  depends  on  the  nature  of  the  ore,  and  the  procedure 
to  be  applied;  thus  we  find  them  made  with  narrow  or  flaring,  deep  or 

2 — GMP 


CALIB'ORNIA    GOLD    MILL    PRACTICES. 


Fig.  17.    Hayward  Mobtae. 


shallow  troughs,  and  with  or  without  inside  plates.  Mortars  with  nar- 
row troughs  are  made  for  greater  output,  while  a  wide  trough  assists 
battery  amalgamation,  and  gives  opportunity  for  placing  inside  copper 
plates.  In  some  of  the  newest  styles  of  mortars  a  series  of  grooves  are 
furnished  in  the  lining  plates,  to  contain  quicksilver.  The  mortars 
weigh  from  4,000  to  6,500  lbs.,  the  bottoms  being  made  extra  heavy;  in 
some  of  the  latest  patterns  the  bottoms  are  8"  thick.  The  length  varies 
between  4^'  and  5',  and  the  height  from  4|'  to  4-i'.  The  inside  width  of 
the  trough  corresponds  with  that  of  the  foot-plate  of  the  dies.  A  heavy 
flange,  4"  x  3",  is  cast  on  the  base  of  the  long  sides,  in  which  are  four 
holes  on  each  side  for  bolts,  to  secure  the  mortar  to  the  block. 

The  difference  in  design  hinges  chiefly  on  the  different  opinions  of 
leading  mining  men  as  to  the  method  and  value  of  amalgamating  inside 
the  battery. 

Figure  17,  known  as  the  Hayward  mortar,  is  a  full-lined  mortar,  with 
flaring  trough,  weighing,  complete,  about  6,500  lbs.,  Avithout  any  special 
arrangements  for  inside  amalgamation. 

Figure  18,  the  Alaska  mortar,  is  a  full-lined  mortar,  with  flaring 
trough,  in  which  the  linings  are  furnished  with  grooves,  to  contain 
quicksilver. 

Figure  19,  the  Wilman's  mortar,  was  the  first  attempt  at  inside  amal- 
gamation, using  an  inside  removable  copper  plate,  but  this  failed  to 
work  well;  the  copper  plate,  being  so  close  to  the  shoe  and  die,  scoured, 
and   could   not   retain    the  amalgam.      In  remedying  this  defect,  the 


CALIFORNIA   GOLD    MILL    PRACTICES. 


19 


?vv.^^^.^-:.-^o^^ 


20 


CALIFORNIA   GOLD    MILL    PRACTICES. 


—  .  ■  •  ^ 


CALIFORNIA   GOLD    MFLL    PRACTICES.  21 

Pacific  mortar  (Fig.  20)  was  produced,  in  which  the  copper  plate  was 
placed  higher  up,  under  the  feed  throat;  experience  in  the  working  of 
which,  suggested  changes  that  finally  evolved  the  Union  mortar  (Fig. 
21),  which  is  provided  with  a  copper  amalgamating  plate,  12"x48", 
bolted  in  a  recess  at  the  back  of  the  mortar,  reaching  below  the  level  of 
the  screen  opening.  This  plate  is  removed  on  clean-up  days  to  be 
scraped,  and  then  replaced.  Similar  good  results  have  been  obtained 
by  the  writer  in  using  a  double-discharge  mortar,  and  filling  the  back 
discharge  opening  with  a  plank  instead  of  a  screen,  to  which  a  plate, 
8"  wide  and  the  length  of  the  opening,  had  been  attached. 

A  modification  of  this  back-plate  arrangement  is  shown  in  the 
accompanying  drawing  (Fig.  22)  of  a  mortar  designed  in  Milwaukee, 
Wis.  Here  the  back  plate  is  accessible,  from  the  back  of  the  mortar, 
through  a  covered  opening;  it  is  secured  in  place  by  a  dovetailed  key 
at  each  end,  allowing  it  to  be  adjusted  to  the  varying  height  of  the  dies. 

Dies  (see  K,  Fig.  8,  and  S,  Fig.  23). — They  consist  of  a  cylindrical 
body  of  the  same  diameter  as  the  shoe,  with  a  square  foot  plate  with 
broken  corners,  and  should  fit  loosely  against  the  front  and  back  plates 
of  the  mortar.  The  broken  corners  permit  their  easy  removal.  They 
are  cast  both  in  iron  and  steel. 

Shoes  (see  J,  Fig.  8,  and  P,  Fig.  23). — They  are  made  of  iron  or  steel, 
and  consist  of  a  cylindrical  body  of  the  same  diameter  as  the  stamp- 
head,  with  a  cone-shaped  neck,  half  as  wide  as  the  cylindrical  body,  and 
about  5"  long.  The  weight  of  the  shoe  bears  a  certain  relation  to  the 
other  parts  of  the  stamp,  generally  about  one  sixth  of  the  total  weight 
when  made  of  chrome  steel,  but  somewhat  less  when  made  of  iron.  The 
cylindrical  portion  of  the  shoe  is  somewhat  longer  than  the  correspond- 
ing part  of  the  die,  on  account  of  its  greater  wear — the  latter  being  pro- 
tected by  a  cushion  of  quartz.  Both  shoe  and  die  are  used  until  worn 
as  thin  as  possible;  with  the  shoe,  this  may  be  i",  though  rarely,  while 
the  die  is  worn  to  the  foot-plate,  if  not  fractured  previously.  This  prac- 
tice is  not- to  be  commended,  and  should  only  occur  in  case  of  necessity. 
On  stamps  weighing  about  900  lbs.  the  shoes,  if  of  chrome  steel,  weigh 
about  150  lbs.,  and  if  of  iron,  weigh  about  20  lbs.  less,  and  are  about  9" 
in  diameter.  The  life  of  the  shoes  depends  on  the  nature  of  the  quartz 
and  the  height  and  speed  of  the  drop,  but  as  a  general  rule  shoes  and 
dies  of  steel  last  as  long  as  two  and  a  half  sets  of  iron  ones,  and  cost 
twice  as  much.  In  the  matter  of  choice  between  steel  and  iron,  the 
vicinity  of  the  mill  to  foundries  is  of  consequence.  Steel  shoes  and  good 
iron  dies  usually  work  very  smooth,  but  where  the  waste  iron  can  be 
disposed  of  at  a  foundry,  this  metal  is  preferred  for  both. 

Stamp-Heads,  Bosses,  or  Sockets  (see  J,  Fig.  8,  and  R,  Fig.  23).-TThey 
are  made  of  cast  iron  or  steel,  of  the  same  diameter  as  the  cylindrical 
part  of  the  sh(ies  and  dies,  with  two  conical  sockets;  the  upper  one 
accurately  bored  out  to  contain  the  tapering  end  of  the  stem,  and  the 
lower  one  to  receive  the  neck  or  shank  of  the  shoe  with  its  inclosing 
circle  of  thin  wooden  wedges.  Transverse,  rectangular  keyways,  at  right 
angles  to  each  other,  pass  through  the  stamp-head  at  the  end  of  the 
conical  openings,  connecting  therewith  in  such  a  manner  that  when  both 
stem  and  shoe  are  attached  to  the  boss  they  protrude  into  the  keyways. 
This  enables  them  to  be  forced  out  by  the  driving  in  of  a  wedge-shaped 


22 


CALIFORNIA   GOLD    MILL    PRACTICES. 


— -"rr^s^ 


'■'■U  -U   ' 


T" 

|l_o 4 

1 
1 

00   Q 

1 
1 

^eJ 

J'- 

7 1 J^ 

CALIFORNIA   GOLD   MILL    PRACTICES.  23 

steel  drift  about  1"  wide,  18"  long,  and  tapering  down  from  2"  toward  the 
point.  The  ends  of  the  stamp-head  are  usually  reinforced  by  having  iron 
bands  shrunk  onto  them. 

Stems  (see  I,  Fig.  8,  and  D,  Fig.  28). — They  are  made  of  wrought  iron 
or  soft  steel,  turned  perfectly  true,  and  tapered  at  both  ends  for  a  dis- 
tance of  6"  or  8".  They  are  from  11'  to  14'  in  length,  the  diameter 
varying  with  the  weight  of  the  stamp  from  2|"  to  3^".  They  are  revers- 
ible, so  that  if  one  end  breaks,  the  other  end  can  be  used  before  sending 
to  the  shop  for  repairs.  When  this  repair  is  made,  the  whole  stem 
should  be  annealed.  The  stem  carries  the  greater  weight  of  any  part 
of  the  stamp,  amounting  to  nearly  one  half.  The  stems  hang  in  the 
guides  at  even  distances  from  center  to  center,  and  are  supported  while 
at  rest  by  props  or  fingers  catching  on  the  under  face  of  the  tappets. 

Tappets  (see  0,  N,  and  0,  Fig.  23). — They  are  made  of  tough  iron  or 
steel,  cylindrical,  with  a  flange  on  both  ends,  and  accurately  bored 
through  the  center,  a  shade  wider  than  the  stem,  and  counter-bored  at 
both  ends;  they  are  provided  with  a  rectangular  recess  adjoining  the 
central  bored  hole,  7"  to  8"  long,  and  from  2"  to  2^"  wide,  in  which  a 
gib  is  fitted.  This  is  a  piece  of  wrought  iron  or  steel,  grooved  on  one 
side,  with  curvature  i"  smaller  than  that  of  the  stem,  and  planed  flat 
on  the  opposite  side.  Two,  or  in  some  cases  three,  slots  are  cut  through 
the  tappet  between  the  flanges,  at  right  angles  to  the  stem,  which  con- 
nect with  the  rectangular  recess  for  the  gib,  so  that  keys,  when  driven 
through  the  slot,  press  the  gib  against  the  stem,  which  should  slide 
smoothly  through  the  center  of  the  tappet.  The  tappets  are  faced  on 
both  ends,  and  are  reversible.  The  keys  are  of  steel,  fitted  and  marked. 
Tappets  weigh  from  100  to  120  lbs.  When  fastening  the  tappet,  the 
keys  are  driven  in  solid;  but  care  must  be  observed,  as  when  too  tightly 
keyed,  the  tappet  is  liable  to  split. 

Cams  (see  C,  C,  Figs.  8  and  23). — They  are  of  tough  cast  iron  or  steel, 
double  armed,  and  strengthened  by  a  hub;  which  latter  is  frequently 
reinforced  by  having  a  wrought-iron  ring  shrunk  on.  The  cam  itself  is 
the  involute  of  a  circle  having  for  its  radius  the  distance  between  the 
center  of  the  stem  and  the  cam-shaft,  somewhat  flattened,  however,  at 
the  point  of  the  cam.  It  comprises  a  face  from  2"  to  3"  wide,  ground 
off,  decreasing  in  thickness  from  the  hub  to  the  point,  and  strengthened 
by  a  rib  on  the  under  side,  which  runs  from  a  point  to  several  inches 
deep  at  the  hub.  The  cam  is  fastened  to  the  cam-shaft  by  steel,  hand- 
fitted  keys. 

Cam- Shafts  (see  A,  Fig.  8). — They  are  made  of  wrought  iron  or  soft  steel, 
turned  true,  with  double  key-seats,  120°  apart  for  cams,  besides  key- 
seats  for  the  driving  pulley.  The  cams  are  slipped  on  the  cam-shaft 
with  the  hub  side  away  from  the  stem,  and  keyed  solidly  in  their  respect- 
ive places;  they  must  be  placed  in  such  a  manner  that  when  the  cams 
are  raising  the  stamps,  the  weight  is  as  nearly  evenly  distributed  over 
the  shaft  as  possible.  For  this  reason  proper  attention  must  be  given 
to  the  sequence  in  which  the  stamps  are  to  drop  in  the  battery.  Where 
the  shaft  is  for  ten  cams,  the  following  order  or  succession  of  drops  is 


24  .  CALIFORNIA    GOLD    MILL    PRACTICES. 

recommended,  viz.:  1,  5,  9,  3,  7 — 10,  6,  2,  8,  4,  and  would  give  a  drop  in 
each  battery  as  follows:  2,  4,  1,  3,  5. 

The  cam,  in  picking  up  a  stem  on  the  under  side  of  the  tappet,  imparts 
a  revolving  motion  to  tappet  and  stem,  requiring  from  four  to  six 
strokes  of  the  cam  to  complete  one  entire  revolution.  A  too  rapid  revo- 
lution indicates  the  need  of  lubricating.  The  revolving  of  the  stem 
assists  in  giving  an  even  wear  to  the  faces  of  the  shoes  and  dies,  but  it 
does  not  impart  a  grinding  action  to  the  stamp,  as  frequently  stated, 
which  can  be  proved  by  holding  a  piece  of  chalk  against  the  stem 
during  its  ascent  and  descent. 

Screens  and  Frames. — Screens  of  different  materials  and  with  different 
orifices  are  used;  the  materials  comprise  wire  cloth  of  brass  or  steel, 
tough  Russian  sheet  iron,  English  tinned  plate,  and,  quite  recently, 
aluminum  bronze.  The  Russian  sheet-iron  plates  are  perforated  with 
round  holes  or  slots;  the  latter  are  vertical,  horizontal,  diagonal,  or 
curved,  and  are  either  entirely  smooth  or  burred  on  the  inner  side.  The 
latter  form  is  intended  for  longer  wear  by  closing  the  burrs  with  a 
mallet  when  too  large,  thereby  prolonging  the  life  of  the  screen. 
These  screens  last  from  fifteen  to  thirty-five  days.  The  plates  have 
glossy,  planished  surfaces,  and  come  in  sheets  of  28"  to  56",  costing  in 
San  Francisco  from  65  to  80  cents  per  square  foot.  The  English  tinned- 
plate  screens  come  in  sheets  of  1'  to  1-i'  square;  they  are  more  flexible 
than  the  Russian  iron,  hence  do  not  permit  of  the  pulp  caking  along 
the  lower  edge  when  fed  high;  and,  as  compared  with  a  Russian  iron 
one  of  the  same  perforations,  they  give  a  greater  discharge,  but  they  are 
short  lived — averaging  about  ten  days.  The  tin  is  burned  off  before 
using.  Brass  screens,  costing  in  San  Francisco  36  cents  a  square  foot, 
are  sold  in  rolls;  they  give  the  greatest  discharge  for  an  equal  area,  and 
last  from  ten  days  to  two  weeks,  but  should  not  be  used  if  cyanide  of 
potassium  be  used  in  the  battery,  on  account  of  clogging  with  amalgam. 
The  "  aluminum  bronze  "  plates  come  in  sizes  similar  to  the  sheet  tinned 
plate,  but  unpunched,  the  latter  work  being  done  here;  they  are  much 
longer  lived  than  either  of  the  other  kinds,  and  have  the  further 
advantage  that  when  worn  out  they  can  be  sold  for  the  value  of  the 
metal  forremelting;  these  plates  are  bought  and  sold  by  the  pound,  and 
are  said  to  contain  95%  of  copper  and  5%  of  aluminum.  Steel-wire 
screens  are  not  much  used,  on  account  of  their  liability  to  rust.  The 
life  of  a  screen  depends,  aside  from  the  manner  of  feeding,  on  the 
width  of  the  mortar,  the  height  of  the  discharge,  and  the  hardness  of 
the  rock.  Wide  mortar  and  high  discharge  are  favorable  to  the  preser- 
vation of  a  screen;  the  form  of  the  perforations — round  holes,  or  slots, 
etc. — influences  the  discharge  area  of  the  screen. 

A  good  deal  of  confusion  exists  in  interpreting  the  numbers  of  the 
different  kind  of  screens.  Wire  screens  take  their  numbers  from  the 
meshes  to  the  linear  inch,  while  perforated  and  slotted  screens  are  num- 
bered from  the  needle  used  in  punching  them,  these  needle  numbers 
being  the  same  as  are  used  for  sewing-machines.  The  sizes  most  fre- 
quently used  in  gold  milling  are  from  No.  6  to  No.  9  of  the  perforated 
and  slotted  screens,  and  from  No.  30  to  No.  40  of  the  wire  screens.  The 
slots  are  from  ■^"  to  -i"  long,  and  placed  alternating  or  even  in  the  rows, 
some  being  burred  on  the  inner  side. 


CALIFORNIA    GOLD    MILL    PRACTICES. 


25 


'tA 


26 


CALIFORNIA   GOLD    MILL    PRACTICES. 


Fig.  25.    Adjustable  Battery  Screen. 

As  dies  wear  down,  wooden  chock-blocks  (on  which  the  inside  plates  are  fixed),  of  less 
height,  are  substitiited,  thereby  preserving  uniformity  in  height  of  discharge. 


CALIFORNIA   GOLD    MILL    PRACTICES.  27 

The  following  table  gives  a  comparison  of  the  different  varieties,  with 
their  numbers: 


No.  of 

Correspondiug 

Width  of  Slot. 

Weight  per  Square 

*Jeedle. 

Mesh. 

(Inches.) 

Foot. 

5 

20 

0.029 

1.15    lbs. 

6 

25 

0.027 

1.08    lbs. 

7 

30 

0.024 

0.987  lbs. 

8 

35 

0.022 

0.918  lbs. 

9 

40 

0.020 

0.827  lbs. 

10 

50 

0.018 

0.735  lbs. 

11 

55 

0.016 

0.666  lbs. 

12 

60 

0.015 

0.666  lbs. 

The  proper  size  required  is  a  matter  for  the  millman  to  decide  at  each 
mill.  The  character  of  the  ore  and  the  coarseness  of  the  gold  have  to  be 
considered,  as  well  as  the  inside  dimensions  of  the  mortar;  ore  carrying 
extremely  fine  gold  requiring  a  finer  crushing,  as  the  gold  must  be  freed 
from  the  quartz  matrix  in  part  if  the  quicksilver  is  to  act  on  it;  but 
where  this  would  lead  to  if  carried  out  to  its  legitimate  end  may  be 
imagined,  when  the  writer  states  that  he  has  observed,  under  the  micro- 
scope, a  particle  of  quartz  that  had  passed  through  a  No.  9  screen  (40- 
mesh)  and  still  contained  several  separate  but  included  particles  of  gold. 
Sulphide  ores,  having  a  much  greater  tendency  to  form  slimes,  should 
be  crushed  as  coarse  as  permissible,  and  where  the  sulphides  predom- 
inate largely,  amalgamation  in  the  battery  is  best  avoided.  The  pulp 
discharged  through  a  screen  carries  but  a  small  percentage  of  the  size  of 
the  orifice;  while  the  largest  proportion  is  much  finer,  it  is  possible  to 
use  a  much  coarser  screen  than  the  size  desired  to  be  obtained  without 
any  great  detriment,  while  greatly  increasing  the  output. 

The  Screen  Fravie  (Figs.  24  and  25). — It  is  made  from  strips  of  sugar 
pine  1^"  by  3"  broad,  mortised,  and  reversible;  usually  they  are  made 
to  close  the  entire  discharge  opening,  grooves  being  cast  on  the  exterior 
of  the  mortar  for  their  reception.  It  is  frequently  strengthened  with 
one  or  more  vertical  ribs  across  the  center  opening,  and  is  faced  with 
iron  plate  on  those  portions  of  the  side  and  bottom  that  come  in  contact 
with  the  iron  keys  that  hold  the  frame  solid  against  the  mortar.  In 
some  mills  the  frame  is  made  several  inches  lower  than  the  opening,  to 
permit  the  millmen  to  observe  the  interior  of  the  mortar  while  in  action, 
and  to  allow  the  hand  to  be  introduced  to  remove  any  chips  that  may 
have  passed  in  with  the  ore,  as  these  have  a  tendency  to  bank  up  against 
the  screen  and  interfere  with  the  discharge  of  the  pulp.  "Where  such  a 
screen  frame  is  used  the  opening  above  is  kept  covered  with  a  strip  of 
canvas  tacked  to  a  wooden  rod,  laid  on  the  upper  projecting  lid,  while 
the  loose  end  of  the  canvas  hangs  against  the  inside  of  the  upper  part  of 
the  screen  frame. 

The  Plate-Block  (Chock-Bloch)  consists  of  wooden  blocks  bolted  solidly 
together,  and  fitted  and  keyed  to  tlie  lower  edge  of  the  mortar  along  the 
discharge  opening,  with  one  part  projecting  above  the  other,  forming  a 
recess  on  top  to  contain  the  screen  frame,  and  lined  with  a  {)iece  of 
blanket  to  make  a  close  joint.  The  inner  side  is  sloped  or  rounded  off, 
and  fitted  with  an  amalgamated  plate.     The  front  and  ends  are  faced 


28  CALIFORNIA   GOLD    MILL    PRACTICES. 

with  iron  plate  to  protect  the  wood.  Two  or  more  sets  of  these  chock- 
blocks  should  be  provided,  of  which  one  stands  2"  higher  than  the  other; 
they  are  then  used  alternately,  the  higher  one  with  new  shoes  and  dies, 
to  be  replaced  by  the  lower  one  when  the  dies  are  worn  down  somewhat, 
to  retain  a  more  even  discharge  than  would  otherwise  be  possible. 

The  Drop  is  the  height  through  which  the  stamp  is  raised  by  the  cam, 
and  through  which  it  drops  when  released.  Usually  it  is  the  same  for 
all  the  stamps  in  a  battery,  although  the  end  and  feed  stamps  sometimes 
receive  a  different  drop.  It  is  regulated  through  the  raising  or  lowering 
of  the  tappet,  and  depends  mostly  on  the  hardness  of  the  rock.  It  is 
one  of  the  factors  in  determining  the  speed  with  which  the  blows  from 
the  stamp  shall  be  repeated.  The  usual  combination  of  the  two  in  the 
California  mills,  is  a  low  drop  with  rapid  motion. 

The  Discharge  is  the  distance  between  the  top  of  the  die  when  in 
place  in  the  mortar,  and  the  lower  edge  of  the  screen  through  which  the 
pulp  discharges.  It  is  one  of  the  most  important  factors  in  the  duty  of 
the  stamps  and  the  gold  output  from  the  ore.  It  should  be  maintained 
as  nearly  as  possible  at  an  even  height  through  the  entire  period  of 
crushing;  the  height  of  the  chock-block  or  screen  frame  being  lowered 
to  correspond  with  the  wear  of  the  die.  A  further  mean?  used  to  retain 
an  even  discharge  is  by  placing  a  2"  iron  plate  under  the  dies,  when 
worn  thin.  The  discharge  stands  in  a  certain  relationship  with  the 
fineness  of  the  screen:  low  discharge  goes  with  coarser  crushing,  a  high 
discharge  with  the  opposite.     The  discharge  varies  in  California  from 

4"  to  id". 

Water  Supply. — Water-pipes  of  3"  diameter  are  brought  along  the 
front  of  the  mortar  near  the  upper  edge,  with  branch  pipes  1"  in 
diameter,  supplied  with  faucets  leading  to  the  feed  side  of  the  mortar, 
to  convey  the  battery  water  in  at  the  back,  or  through  the  plank-cover- 
ing on  the  top;  this  water  is  under  moderate  pressure.  A  second  dis- 
charge pipe  is  carried  down  in  front  to  the  lower  lip  of  the  mortar, 
where  a  movable,  perforated  branch  is  turned  across  the  front  of  the 
screen,  discharging  along  the  entire  line  on  the  lip;  this  second  dis- 
charge pipe  also  supplies  a  hose.  The  battery  water  should  enter  both 
sides  of  the  mortar  in  an  even  quantity,  and  the  total  amount  must  be 
sufficient  to  keep  a  fairly  thick  pulp  that  discharges  freely  through  the 
screen.  About  120  cu.  ft.  of  water  per  ton  of  crushed  ore  may  be  con- 
sidered an  average,  or  8  to  10  cu.  ft.  per  stamp  per  hour. 

Aprons  and  Apron-Plates. — The  apron  is  a  low  table  placed  in  front 
of  the  mortar,  just  below  and  in  immediate  proximity  to  the  lower  lip 
of  the  discharge,  for  the  reception  of  amalgamated  copper  plates.  It  is 
set  on  a  sufficient  grade  to  permit  the  discharging  pulp  to  flow  over  it  in 
an  even  stream,  while  affording  the  suspended  amalgam  an  opportunity 
to  reach,  and  adhere  to,  the  plate  surface.  The  size,  shape,  and  slope 
are  at  the  will  of  the  millman;  but  usually  they  are  rectangular,  with 
the  plates  screwed  down  to  the  table  with  copper  screws,  perfectly  level 
and  smooth,  the  sides  being  secured  with  wooden  cleats.  The  grade 
given  varies  from  -i"  to  2V'  to  the  foot,  and  the  width  of  the  apron  is 
usually  the  width  of  the  discharge-opening  of   the  mortar.     In  some 


CALIFORNIA   GOLD    MILL    PRACTICES. 


29 


mills  several  of  these  apron-plates  are  placed  consecutively,  discharging 
from  one  to  the  other.  They  are  usually  rigid,  but  in  some  instances 
the  apron  next  to  the  mortar  stands  on  rollers,  permitting  it  to  be 
rolled  back,  and  thus  giving  freer  access  to  the  front  of  the  mortar. 
They  should  not  be  attached  to  the  battery  frame. 

Sluices  and  Sluice-Plates. — These  vary  from  12"  to  20"  in  width,  and 
are  placed  below  the  aprons;  they  are  usually  set  to  a  grade  different 
from  that  of  the  apron.  The  plates  can  be  fastened  by  cleats,  or  are 
laid  overlapping  at  the  ends,  and,  if  not  wider  than  16",  do  not  need 
to  be  fastened  down  with  side  cleats;  this  permits  of  their  being  picked 
up  and  cleaned  at  any  time  without  stopping  the  battery.  The  sluices 
are  rarely  over  16'  long — more  frequently  in  lengths  of  8' — and  should 
always  be  placed  double.  The  width  and  grade,  as  compared  with  the 
apron  areas,  are  mostly  faulty  in  California  mills.- 


g"   i»Wh,  r^  ■ 


Fig.  26.    Clean-up  Barrel. 

Clean-up  Barrel. — Large  mills  are  supplied  with  clean-up  barrels, 
which  consist  of  iron  barrels  supported  by  trunnions  resting  in  bearings 
on  short  standards.  One  of  the  trunnions  is  extended  to  carry  a  loose 
and  a  tight  pulley,  by  means  of  which  it  is  revolved.  A  manhole,  with 
tight-fitting  cover,  is  provided  for  charging  and  discharging,  and  below 
it  is  a  sluice  with  cross-riffles  to  receive  the  pulp  when  discharged  from 
the  barrel.  The  barrel  should  make  from  thirty  to  forty  revolutions  a 
minute,  requiring  2^  H.  P.  It  is  used  to  treat  the  battery  sands  when 
cleaning  up  the  mill;  also,  all  the  scrapings  from  the  mill  floors,  as  well 
as  sand  from  the  drop  boxes  and  amalgam  traps,  large  pieces  of  quartz 
or  pieces  of  broken  shoes  being  added  with  water  and  quicksilver  to 
assist  in  the  operation. 

Clean-up  Pan  (Fig.  27). — This  is  a  small  amalgamating  pan,  3'  to  4' 
in  diameter,  operating  with  muUcrs  with  wooden  shoes,  and  is  run  at  a 
speed  of  thirty  revolutions,  requiring  1^  H.  P.  When  in  use  the  pan  is 
half  filled  with  water,  and  the  amalgam  put  in,  with  an  addition  of  clean 


30 


CALIFORNIA    GOLD    MILL    PRACTICES. 


quicksilver,  and,  if  required,  also  some  lye.  After  sufficient  grinding, 
the  muddy  water  is  run  out  through  plug-holes,  the  mullers  stopped, 
and  the  contents  drawn  off  in  buckets.  The  iron  found  floating  on  top 
of  the  quicksilver  is  removed  with  a  magnet;  the  sand  is  washed  off 
with  a  small  stream  of  clear  water,  and  if  any  dross  be  found  covering 
the  surface  it  is  skimmed  otF  with  a  sponge  or  piece  of  blanket. 


Fig.  27.    Clean-up  Pax. 

Cleaning-up  Room. — This  is  an  apartment  in  close  proximity  to  the 
batteries  and  aprons,  provided  with  a  tight  floor,  and  with  a  door  under 
lock  and  key;  the  floor  is  best  when  laid  in  cement,  to  avoid  all  losses 
from  split  quicksilver  or  amalgam.  It  should  be  well  lighted,  and  fur- 
nished with  a  sloping  table  large  enough  to  place  a  screen  frame  on; 
also,  with  one  or  two  water-tight  boxes  about  4'  long,  3'  wide,  and  3' 
deep,  for  panning-out  purposes;  these  are  supplied  with  plug-holes  near 
the  bottom,  to  drain  off  the  water,  besides  water-pipes  and  fittings  to  fill 
the  boxes  when  required.  One  or  two  wide  shelves  should  be  provided 
to  hold  the  chemicals,  quicksilver,  and  utensils  needed  in  cleaning  up. 
The  latter  consist  of  pans,  wedgewood  mortar,  brushes,  scoops,  cups, 
knives,  chisels,  rubbers,  scrapers,  and  a  supplv  of  closely  woven  drilling 
or  light  canvas;  the  latter  is  used  to  squeeze  the  superfluous  quicksilver 
from  the  amalgam.  A  good  pair  of  balances,  wdth  a  set  of  accurate 
weights,  oapable  of  weighing  the  amalgam  and  the  retorted  bullion, 
should  also  be  provided.  The  table  should  be  made  of  a  solid  plank,  or 
a  slab  of  slate  or  marble,  supplied  with  a  raised  edge,  and  grooved 
around  to  drain  into  a  pan  placed  on  a  shelf  attached  below  the  lower 
end;  some  tables  are  covered  with  an  amalgamated  plate.  It  is  some- 
times convenient  to  have  a  small  safe  in  the  clean-up  room,  but  it  is 
always  better  to  have  the  amalgam  delivered  to  the  office. 


CALIFORNIA   GOLD    MILL    PRACTICES. 


31 


Fig.  28.    The  Kxight  Wheel. 


POWER    FOR    MILLS. 


On  account  of  the  favorable  position  of  the  majority  of  California 
mines  as  regards  their  proximity  to  mountain  streams  and  the  large 
ditch  systems,  the  application  of  water  for  the  motive  power  of  the  mills 
is  rendered  easy,  and  where  the  distance  from  these  sources  is  remote, 
electricity  generated  in  such  localities  and  transmitted  to  the  mill  is 
being  successfully  applied.  Where  steam  power  has  to  be  used,  the  well- 
timbered  western  slopes  of  the  Sierra  Nevada  permit  the  cost  of  fuel  to 
be  kept  at  a  comparatively  low  figure.  Where  both  water  and  timber 
are  hard  to  obtain,  as  in  the  desert  regions  of  the  southern  part  of  the 
State,  gas  engines  have  been  applied  with  most  satisfactory  results. 

In  applying  water  power,  where  the  pressure  is  sufficient,  hurdy-gurdy 
wheels  are  chiefly  used;  these  are  vertical  wheels  with  narrow  breasts, 
having  buckets  of  various  patterns  radially  attached  to  the  outer  cir- 
cumference, the  water  being  projected  through  one  or  more  nozzles 
against  the  buckets  at  a  low  point  of  the  wheel,  allowing  the  water  to 
pass  from  the  buckets  as  soon  as  the  blow  has  been  delivered.  The 
principal  patterns  in  actual  use  are  the  Knight,  Pelton,  and  Dodds;  the 
actual  effective  power  developed  by  the  Pelton  buckets  is  given  at  about 
75%  to  80%.  Where  sufficient  pressure  cannot  be  obtained,  the  Leffel 
turbine  and  the  overshot  wheel  are  in  use.  As  the  Pelton  wheel  seems 
to  find  the  most  frequent  application  in  California,  it  may  be  convenient 
for  millmen  to  have  the  following  rule,  applicable  to  these  wheels:  When 
the  head  of  water  is  known  in  feet,  multiply  it  by  0.0024147,  and  the 
product  is  the  horse- power  obtainable  from  one  miner's  inch  of  water. 


32 


CALIFORNIA    GOLD    MILL    PRACTICES. 


Fig   29     The  PELTO^  "\V\ter  Wheel. 

The  power  necessary  for  different  mill  parts  is: 

For  each  850  lb.  stamp,  dropping  6"  95  times  per  minute L33  H.P. 

For  each  750  lb.  stamp,  dropping  6"  95  times  per  minute 1.18  H.P. 

For  each  650  lb.  stamp,  dropping  6"  95  times  per  minute 1.00  H.P. 

For  an  8"xl0"  Blake  pattern  rock-breaker 9.00  H.P. 

For  a  Frue  or  Triumph  vanner,  with  220  revolutions  per  minute 0.50  H.P. 

For  a  4'  clean-up  pan,  making  30  revolutions 1.50  H.P. 

For  an  amalgamating  barrel,  making  30  revolutions 2.50  H.P. 

For  a  mechanical  batea,  making  30  revolutions 1.00  H.P. 


MILL    PRACTICES. 


Where  the  conditions  permit,  it  is  becoming  the  custom  to  place  the 
grizzly  and  the  rock-breaker  in  close  proximity  to  the  hoist,  so  that 
the  bucket  or  car  on  arriving  at  the  surface  is  dumped  direct  on  a 
grizzly,  and  the  crushed  ore  is  then  run  over  the  ore-bin  in  the  mill, 
and  emptied  therein;  where  this  is  impracticable,  the  grizzly  and  rock- 
breaker  are  placed  over  the  ore-bin  in  the  mill. 

The  usual  practice  is  to  let  the  coarse  ore  from  the  grizzly  drop  on  a 
platform  on  a  level  with  the  mouth  of  the  rock-crusher,  into  which  it  is 
shoveled  by  hand;  by  this  method  the  machine  is  not  brought  up  to  its 
full  capacity.  A  better  plan  is  to  convey  the  coarse  ore  from  the  grizzly 
into  the  bin  by  means  of  a  chute,  having  a  sliding  gate  immediately 
above  the  receiving  point  of  the  crusher,  and  which  is  set  so  as  to  keep 
the  space  between  the  jaws  always  filled.  In  this  way  the  work  becomes 
automatic,  and  the  services  of  the  man  attending  the  rock-breakers  can 
be  utilized  in  other  parts  of  the  mill  during  part  of  the  time.  Under 
such  an  arrangement  the  crusher  will  require  more  power,  which  should 
be  independent  from  the  other  machinery.  The  rock-breaker  is  usually 
run  during  the  daytime  only,  as  it  can  crush  in  that  time  enough  ore 
for  the  mill  for  the  twenty-four  hours. 

The  self-feeders,  in  a  similar  manner,  are  kept  automatically  filled 


CALIFORNIA    GOLD    MILL   PRACTICES.  33 

from  the  main  ore-bin.  The  feeding  through  the  tappet  striking  on  the 
bumper-rod  of  the  self-feeder,  has  of  late  been  modified.  A  collar  is 
fastened  below  the  guides  on  the  feed-stamp  stem,  taking  the  place  of 
the  tappet,  thus  avoiding  the  long  bumper-rod.  The  gauging  of  the 
feed  must  be  carefully  attended  to,  if  the  stamps  are  to  work  up  to  their 
full  capacity;  there  should  never  be  more  than  about  1"  of  rock  between 
the  stamp  and  die  when  they  come  together,  or  the  feed  should  be  just 
sufficient  to  keep  iron  from  striking  iron.  When  cleaning  up  the  bat- 
teries, the  self-feeders  are  drawn  back  on  a  track  toward  the  ore-bin, 
giving  access  to  the  back  of  the  mortars. 

In  preparing  the  mortar  for  Ore-crushing,  an  inch  or  two  of  tailings 
is  spread  evenly  over  the  bottom  before  putting  the  dies  in  place,  as  this 
saves  the  wear  on  the  bottom  plate.  After  the  dies  are  placed  exactly 
under  each  stamp,  crushed  ore  and  fine  rock  are  banked  around  them  to 
retain  them  in  proper  place  until  the  sands  have  settled  firmly  about 
them.  Care  must  be  observed  to  keep  the  tops  of  all  the  dies  at  the 
same  level  at  all  times,  as  otherwise,  when  the  stamps  are  dropping  the 
highest  die  will  strike  against  iron,  while  the  others  are  still  supplied 
with  sufficient  ore;  this  is  known  as  "pounding." 

The  stamp-head,  or  boss,  is  now  placed  on  the  die  with  the  small  con- 
ical opening  at  the  top,  and  the  stem  lowered  into  it,  iron  against  iron  if 
it  is  a  close  fit,  and  driven  in  solid.  In  case  the  connection  is  not  tight, 
canvas  strips  about  2"  wide  are  laid  crosswise  over  the  opening  before 
the  stem  is  lowered.  The  stem,  with  the  stamp-head,  is  now  raised 
until  the  latch-finger  catches  under  the  lower  face  of  the  tappet  and 
holds  them  suspended,  and  the  shoe  placed  on  the  die.  If  the  stamp- 
head  hangs  too  low  to  permit  of  this,  the  stem  is  raised,  and  a  block 
placed  on  top  of  the  finger  for  the  tappet  to  rest  on.  Narrow  wooden 
wedges,  about  1"  wide,  the  length  of  the  neck  of  the  shoe,  and  of  the 
requisite  thickness  to  fit  tightly  into  the  conical  opening  at  the  bottom 
of  the  stamp-head,  are  arranged  in  place  and  tied  with  a  string.  The 
block  and  finger  are  then  removed,  the  stamp-head  dropped  over  the 
shank,  and  wedges  driven  down  firmly.  This  is  done  best  by  revolving 
the  cam-shaft  slowly,  and,  while  placing  the  cam-stick  between,  permit- 
ting the  cam  to  act  on  the  tappet,  raising  and  dropping  the  stamp  until 
the  lower  edge  of  the  stamp-head  is  nearly  in  contact  with  the  shoulder 
of  the  stamp.  It  is  not  advisable  to  permit  them  to  come  solidly  together, 
as  it  tends  to  loosen  the  iron  ring  that  reinforces  the  stamp-head.  A 
quick  and  convenient  method  of  placing  the  wooden  wedges  on  the  shoe, 
is  to  cut  a  piece  of  canvas  to  fit  exactly  around  the  neck,  and  attach 
the  wedges  to  the  canvas  by  driving  a  tack  through  each  one  into  the 
cloth.  By  keeping  a  supply  of  these  on  hand,  it  becomes  an  easy  mat- 
ter to  encircle  the  shank  on  the  shoe  and  tie  them  fast,  should  the  shoe 
become  loose  and  drop  ofi"  while  the  mill  is  running. 

The  Drop. — The  next  operation  is  fixing  the  distance  through  which 
the  stamp  is  to  drop  before  striking  the  die.  In  most  mills  this  dis- 
tance is  uniform  for  all  the  stamps;  but,  as  previously  stated,  occa- 
sionally the  stamp  operating  the  feed,  as  also  the  two  outside  stamps, 
receive  a  greater  drop. 

The  right  height  to  give  depends  on  the  nature  of  the  ore,  as  also  on 
the  speed  to  be  given  to  the  stamps;  that  is,  the  number  of  drops  per 
minute.     The  tendency  in  most  California  mills  is  to  run  at  a  high  rate 

3 — QMP 


k 


34 


CALIFORNIA   GOLD    MILL    PRACTICES. 


of  speed,  usually  in  the  neighborhood  of  one  hundred  drops  per  minute. 
The  height  varies  from  4"  to  about  10",  generally  but  little,  if  any, 
above  the  water-level  in  the  mortar. 

In  arranging  the  stamps  for  an  equal  drop,  wooden  blocks,  cut  about 
^"  longer  than  the  drop  the  stamps  are  to  receive  to  permit  the  cams  to 
clear  the  tappets,  are  placed  on  the  die,  between  it  and  the  shoe. 
Pieces  of  2  x  4  scantling,  cut  to  the  desired  length,  answer  well  for  the 
purpose.  The  keys  in  the  tappet  are  loosened  with  a  drift  made  of  steel, 
the  size  of  the  keyholes,  and  used  only  for  that  purpose,  and  the  stem 
is  allowed  to  slip  through  the  tappet  until  the  shoe  rests  on  the  top  of 
the  wooden  block  beneath;  or,  if  the  shoe  was  resting  on  the  block 
previously,  the  tappet  is  slipped  up  till  resting  on  the  latch-finger,  when 
the  keys  are  driven  home  solid.  Care  must  be  exercised  not  to  drive 
the  keys  too  solid,  else  there  is  danger  of  splitting  the  tappet.  For  the 
convenience  of  the  millman,  a  chalk  mark  is  made  around  the  stem  just 
above  the  tappet,  which  enables  him,  while  running,  to  at  once  detect  if 
any  of  the  tappets  have  slipped.  Should  this  occur  it  must  be  imme- 
diately re-set,  or  the  battery  work  will  be  irregular.  The  battery-plates 
and  chock-blocks  are  next  put  in  place  and  keyed. 

The  Discharge  is  next  arranged.  This  is  the  distance  between  the  top 
of  the  new  dies  and  the  lower  edge  of  the  screen,  and  to  fix  the  right 
distance  is  of  importance.  The  greater  the  height  of  the  discharge,  the 
greater  will  be  the  proportionate  amount  of  pulp  and  slime,  and  they 
also  will  be  retained  longer  in  the  mortar.  The  quantity  of  amalgam 
retained  in  the  mortar  is  also  proportionately  greater.  A  low  discharge 
calls  for  a  coarser  screen,  and  naturally  results  in  a  larger  output  of  the 
battery,  and  with  a  larger  proportion  of  outside  plate  amalgam.  With 
a  constant  height  of  the  screen,  the  natural  wear  of  the  die  increases  the 
height  of  the  discharge.  For  ordinary  iron  shoes  and  dies,  and  average 
rock,  the  wear  of  the  die  is  roughly  estimated  from  -f  to  1  lb.  of  iron  per 
ton  of  ore  crushed.  To  counteract  the  efiect  of  this  wear  on  the  discharge 
height,  different-sized  chock-blocks  or  screen-frames  are  supplied;  the 
highest  being  used  with  new  dies,  and  later  replaced  by  lower  ones,  thus 
holding  the  distance  more  even  than  the  use  of  a  single  size  would  per- 
mit. In  some  mills,  when  the  dies  are  worn  down,  an  iron  plate,  made 
fot  the  purpose,  is  laid  beneath  them  to  raise  them  up. 

As  a  very  high  discharge,  besides  creating  much  slime,  beats  up  a 
larger  portion  of  the  gold  into  float  gold  than  would  be  the  case  with 
low  discharge,  the  choice  necessarily  influences  the  gold  recovery;  this 
is  more  particularly  the  case,  if  the  ore  carries  any  appreciable  amount 
of  valuable  sulphurets.  The  discharge  varies  in  the  different  mills  from 
4"  to  10",  the  average  being  from  6"  to  7". 

Screens. — In  fastening  the  screen  to  the  screen-frame,  care  must  be 
observed  to  get  it  on  smooth,  without  any  wrinkling  or  buckling.  Tin 
screens  must  have  the  tin  burned  off  before  fastening  to  the  frame;  it  is 
also  well  to  expose  the  Russian-iron  screens  to  a  quick  fire  of  shavings, 
to  burn  off  the  oil  with  which  they  are  more  or  less  faced.  The  edges 
of  the  screens  are  tacked  to  the  frames,  and  are  faced  with  strips  of 
blanket  to  make  a  close  connection  with  the  mortar.  In  fastening  a 
wire-cloth  screen,  to  get  it  on  smooth,  a  good  method  is  to  tack  it  first 
along  the  lower  edge,  then  draw  it  up  tight  and  even  over  the  upper 


CALIFORNIA   GOLD    MILL    PRACTICES.  35 

edge,  and  nail  it  before  cutting  it  off  the  roll.  As  previously  stated, 
brass-wire  screens  should  not  be  used  in  conjunction  with  cyanide  of 
potassium,  as  the  brass  becomes  coated  and  clogged  with  amalgam. 
The  screen-frame  with  screen  is  dropped  into  the  grooves  cast  on  the 
outside  of  the  mortar  discharge,  and  fastened  solid  with  iron  wedges — 
two  vertical  (one  for  each  groove)  and  a  horizontal  one  in  the  center  of 
the  lower  lip.  The  wedges  should  have  a  broad  head,  to  facilitate 
knocking  them  out.  After  the  screen  has  been  fastened  in  place,  a 
piece  of  canvas  or  a  board  should  be  hung  in  front  to  arrest  the  out- 
ward throw  of  the  pulp  from  the  drop  of  the  stamp,  and  direct  it  in  an 
even  flow  onto  the  plates  beneath.  In  some  mills  this  board  is  given 
a  slope  toward  the  screen,  and  has  an  amalgamated  plate  screwed  on, 
which  receives  the  splash.  Bolted  to  the  front  of  the  modern  mortars 
is  a  frame  to  carry  the  outside  battery-plate  and  a  distributing-box,  a 
few  inches  above  the  apron-table  on  which  it  discharges. 

When  everything  is  ready  to  drop  the  stamps,  the  self-feeder  is  rolled 
to  its  place,  the  cam-shaft  is  set  to  revolving  slowly,  the  water  is  turned 
into  the  battery,  and  the  millman,  standing  on  the  platform  above, 
grasps  the  hand-hold  of  the  first  finger  or  prop  and  introduces,  with  the 
other  hand,  the  cam-stick  between  the  tappet  and  the  revolving  cam;  by 
this  means  the  weight  of  the  stamp  is  taken  off  the  prop,  which  is  pulled 
back  and  rested  against  the  edge  of  the  platform.  This  operation  is 
repeated  with  each  stamp  until  all  are  working.  To  carry  out  this 
operation  when  the  shaft  is  revolving  rapidly,  without  injuring  the 
operator's  hands,  requires  practice.  The  cam-stick  mentioned  above 
consists  of  a  piece  of  wood  about  2^'  long,  1"  thick  at  the  point,  running 
up  to  2^"  near  the  handle,  and  faced  with  strap-iron  or  a  strip  of  belt- 
ing. It  may  also  be  made  entirely  of  strips  of  belting,  2"  or  3"  wide, 
nailed  over  each  other  and  attached  to  a  wooden  handle.  To  hang  up 
the  stamps,  the  hand-hold  is  grasped,  the  knee  pressed  to  the  latch- 
finger,  and  the  cam-stick  introduced  between  cam  and  tappet  as  before, 
and  the  latch-finger  pushed  under  the  tappet. 

Before  dropping  the  stems  the  face  of  the  cams  should  be  lightly 
lubricated,  for  which  purpose  axle  grease  or  specially  prepared  com- 
pounds are  used;  a  very  useful  one  is  a  mixture  of  graphite  and  molasses; 
in  some  mills,  to  avoid  the  use  of  grease,  the  face  of  the  cam  is  rubbed 
with  a  bar  of  common  soap. 

Grease. — It  being  essential,  for  good  amalgamation,  that  the  presence 
of  grease  be  avoided  in  the  battery,  care  must  be  observed  in  lubricat- 
ing the  cams,  the  stems  where  passing  through  the  guides,  and  the 
shaft  bearings.  In  many  mills,  trays  made  from  old  oil-cans  are 
fastened  beneath  the  bearings,  cloth  aprons  are  tacked  from  the  under- 
side of  the  guides  to  the  floor  above;  rings  of  rubber  packing  or  old 
belting  also  encircle  the  stems  at  the  lower  edges  of  the  guides.  The 
millman  should  diligently  wipe  off  the  stems  and  any  part  of  the  battery 
frame,  where  the  presence  of  grease  is  indicated,  at  least  once  during 
a  shift.  Grease  in  the  mortar  is  indicated  by  a  black,  dirty  appearance 
of  the  surface  of  the  plates,  as  also  by  the  adhesion  of  more  than  the 
usual  proportion  of  the  amalgam  to  the  iron  castings  inside  the  mortar. 
The  usual  remedy  is  to  shut  off  a  part  of  the  battery  water,  for  a  short 
time,  while  adding  a  lye  solution;  or  to  add  fine  wood  ashes  to  the  ore. 


36  CALIFORNIA    GOLD    MILL    PRACTICES. 

The  Amount  of  Water  Required  for  the  proper  working  of  the  battery 
depends  on  the  nature  of  the  ore;  clayey  ores,  or  such  as  have  a  high 
percentage  of  sulphurets,  requiring  the  most;  but  while  in  the  former 
case  a  greater  amount  is  needed  inside  the  mortar,  the  latter  condition 
permits  a  part  being  added  outside  the  screen,  on  the  lip  of  the  mortar. 
A  small  sluice-box,  with  plug-holes,  is  placed  across  the  front  in  this 
case,  or  the  water  is  conveyed  by  means  of  a  half-inch  perforated  iron 
pipe,  attached  to  the  vertical  supply  pipe  by  an  elbow  joint,  permitting 
it  to  be  turned  either  way  as  required.  "The  amount  of  water  used  per 
ton  of  ore  stamped  varies  from  1,000  to  2,400  gallons,  with  a  mean 
amount  of  about  1,800  gallons  per  ton  of  rock  crushed."  *  Most  of  the 
mills  in  actual  practice  figure  roughly  on  one  miner's  inch  of  water, 
more  or  less,  per  twenty-four  hours  for  each  battery  of  five  stamps.  To 
obtain  the  largest  amount  of  crushing  of  clean  quartz  from  a  battery, 
only  sufficient  water  should  be  used  inside  to  keep  up  the  regular,  even 
swash  of  the  pulp,  and  if  that  be  not  sufl&cient  to  keep  the  plates  on  the 
outside  clear  from  accumulating  pulp,  more  may  be  added  outside  the 
the  screen.  The  pulp,  in  passing  down  over  the  apron-plate,  should  roll 
in  successive  waves,  corresponding  to  the  back  and  forth  wave-motion 
inside  the  battery,  rather  than  flow  in  an  even  sheet,  as  affording  a 
better  opportunity  of  contact  for  the  particles  of  amalgam. 

Where  the  temperature  falls  low  in  winter,  arrangements  should  be 
made  to  deliver  the  water  in  a  tepid  condition,  as  better  amalgamating 
results  will  be  obtained,  through  keeping  the  quicksilver  in  a  lively 
condition.  Where  steam  power  is  used,  this  can  be  easily  arranged;  but 
when  using  water  power,  a  separate  heater  is  required. 

Feeding. — Hand-feeding  has  become  nearly  obsolete  in  California. 
It  is  only  practiced  in  small  concerns,  or  where  a  temporary  mill  has 
been  put  up  for  prospecting  purposes.  The  advantages  of  a  machine- 
fed  mill  are  numerous;  the  chief  of  these  are  (1)  that  the  wear  of  the 
iron  of  the  shoes  and  dies  is  less  and  more  even-faced;  (2)  that  from 
15%  to  20%  more  ore  can  be  crushed  in  a  given  time;  and  (8)  that  the 
labor  expenses  are  reduced.  The  machines  should  be  carefully  gauged 
and  watched  to  insure  a  steady,  low  feeding  of  the  stamps.  In  order  to 
insure  a  good  splash  in  the  mortar  attention  must  be  given  to  the  suc- 
cession in  which  the  stamps  are  made  to  drop.  A  good  splash  is  one 
that  shows  a  wave  passing  along  the  lower  edge  of  the  screen,  moving 
backward  and  forward  from  end  to  end,  or  a  similar  wave-motion  that 
has  its  initial  point  from  the  center  stamp.  The  succession  most  fre- 
quently adopted  in  California  is  3,  5,  1,  4,  2;  1,  5,  2,  4,  3;  1,  3,  5,  2,  4, 
and  1,4,  2,  5,  3;  the  last  spreads  the  pulp  very  evenly  from  end  to  end. 
The  greatest  amount  of  discharge  is  obtained,  apparently,  by  dropping 
the  center  stamp  first;  while  the  most  crushing  is  done,  other  conditions 
being  equal,  by  dropping  the  end  ones  first.  Any  arrangement  of  the 
stamps  will  answer,  however,  that  distributes  the  pulp  evenly  and  dis- 
charges it  well. 

The  Apron  should  be  set  immediately  in  front  of  the  mortar,  but 
independent  of  the  battery-frame,  to  exempt  it  from  the  jar  of  the 
stamps;  it  should  be  arranged  to  permit  of  the  grade  being  easily 
altered  if  necessary.     The  size,  shape,  and  grade  of  the  apron-plates 

*See  Ylllth  Report  of  State  Mineralogist,  p.  710. 


CALIFORNIA  GOLD    MILL    PRACTICES.  37 

diflfer  widely,  depending  largely  on  the  millman's  preferences  and  experi- 
ence. The  usual  form  of  the  apron  is  rectangular,  of  the  width  of  the 
discharge,  and  any  length  desired,  but  usually  from  4'  to  12',  forming  a 
level  (transversely),  smooth  surface,  set  on  a  grade  varying  from  ^"  to 
2^"  to  the  foot.  Sometimes  the  surface  is  divided  by  steps,  with  or  with- 
out distributing-boxes.  These  are  usually  from  1"  to  2".  The  apron 
should  never  be  drawn  in  at  the  lower  end,  for  reasons  given  farther  on; 
and  the  steps  should  not  be  too  deep,  as  otherwise  the  plate  next  to  the 
drop  will  show  mostly  bare  copper  through  scouring. 

On  examining  a  plate  that  is  in  use  under  good  working  conditions, 
it  will  appear  that  the  upper  portion,  immediately  below  the  mortar,  say 
for  a  distance  of  18",  carries  at  least  75%  of  all  the  amalgam  caught  on 
the  apron,  the  largest  accumulation  showing  along  the  line  of  impinge- 
ment next  the  lip  of  the  mortar.  Now  if  the  apron-plate  were  discon- 
tinued at  about  2',  and  continued  again  on  a  lower  level  of  about  2",  a 
second  line  of  accumulation  would  result,  naturally  on  a  smaller  scale; 
hence,  the  advantage  of  the  step  form.  Another  advantage  in  this  style 
of  apron,  is  that  by  fastening  these  sections  to  the  table  by  means  of 
wooden  buttons  on  the  sides  instead  of  cleats  and  screws,  and  having 
one  extra  plate  on  hand,  the  scraping  and  dressing  of  the  same  can  be 
performed  at  any  time,  without  stopping  the  crushing  of  the  stamps,  by 
removing  the  plate  and  substituting  the  extra  one. 

The  grade  of  the  apron-plate  should  be  such  as  to  keep  the  surface 
clear  from  any  pulp  accumulations,  but  not  steep  enough  to  obtain  a 
scouring  action.  It  will  depend  on  the  coarseness  of  the  pulp,  the 
nature  of  the  gold,  the  amount  of  water  available,  and  the  percentage 
and  nature  of  the  sulphurets.  Where  a  battery-plate  is  in  use  above 
the  apron,  it  is  usually  given  a  grade  of  from  1^"  to  2"  to  the  foot. 
Grades  for  the  apron  proper  vary  from  i"  to  2^"  to  the  foot,  but  the 
average  is  about  1|".  The  apron-plates  are  usually  silver-plated  copper 
plates,  which  have  largely  superseded  the  copper  amalgamated  plate  of 
former  days — chiefly  on  account  of  the  readiness  with  which  the  former 
plates  do  their  full  duty  from  the  first  starting,  which  is  not  the  case 
with  the  copper  plate;  also,  on  account  of  their  freedom  from  discolora- 
tion by  oxidation.  If  silvered  plates  be  used  when  running  a  very 
low-grade  ore,  the  plating  soon  wears  off,  requiring  a  replating  about 
every  six  months.  The  usual  amount  of  silver  put  on  plates  is  one 
ounce  to  the  square  foot.  The  usual  thickness  of  copper  plates  is  yV' 
to  g-".  In  preparing  them  for  amalgamation  they  should  first  be  care- 
fully heated  to  a  black  heat,  and  plunged  into  cold  water,  which  makes 
them  soft  and  more  ready  to  take  up  quicksilver.  They  are  then  scoured 
bright  with  fine  tailings-sand,  moistened  with  some  cyanide  of  potassium, 
and  applied  with  a  block  of  wood;  then  dressed  all  over  with  a  weak 
solution  of  nitric  acid,  or  with  cyanide  of  potassium  and  quicksilver, 
with  sodium  amalgam  sprinkled  over  and  brushed  or  rubbed  into  the 
surface.  Before  final  use,  it  is  well  to  give  them  a  coating  of  fine  gold 
amalgam;  or,  if  not  convenient,  silver  amalgam  will  answer.  In  using 
the  cyanide  of  potassium  solution,  care  must  be  taken  not  to  use  it  too 
strong,  especially  if  the  quicksilver  is  not  applied  to  the  plate  im- 
mediately, otherwise  a  coating  is  formed  on  the  surface  that  will  not 
take  up  the  quicksilver.  Where  the  ore  is  of  a  fair  grade,  after  a  long 
period  of  continuous  use  the  plate  will  have  absorbed  an  amount  of  gold 


OS  CALIFORNIA    GOLD    MILL    PRACTICES. 

that  will  not  yield  to  scraping  unless  the  plate  is  immersed  in  boiling 
water  for  a  time  before  being  scraped,  or  heated  over  a  fire  and  ham- 
mered with  a  mallet  on  the  reverse  side,  in  which  case  care  must  be 
taken  not  to  dent  the  plate. 

As  the  saving  of  amalgam  on  the  apron  and  sluice-plates  is  largely  a 
matter  of  gravity,  the  conditions  under  which  the  pulp  passes  over  the 
plates  should  conform  to  the  laws  pertaining  to  the  falling  of  a  body 
through  a  moving  liquid  medium;  hence  the  proper  shape  of  the  apron, 
and  the  flow  and  consistency  of  the  pulp,  should  be  well  considered.  If, 
as  was  formerl}^  the  almost  universal  custom,  the  lower  end  of  the  apron 
be  contracted  (and  in  numerous  cases  this  contraction  was  as  great  as 
four  to  one),  the  depth  of  the  pulp  spread  over  the  surface  of  the  plate 
increases  as  it  passes  down;  the  flow  of  the  water  across  a  given  section 
becomes  uneven,  forming  at  the  sides  a  swirl,  along  the  edge  of  which, 
sand  is  precipitated,  covering  and  rendering  that  portion  of  the  plate 
useless,  from  its  inability  to  come  in  contact  with  the  particles  of 
amalgam,  while  producing  scouring  currents  at  other  parts.  The  proper 
method  is  to  spread  the  flow  over  a  wider  surface  as  it  passes  from  one 
plate  to  the  other,  and  lessen  the  grade,  which  may  require  an  addition 
of  clear  water. 

This  contraction  of  the  plates  is  made  to  this  day  in  most  of  the 
mills,  when  connecting  with  the  sluice-plates.  The  liquid  pulp,  starting 
with  a  width  equal  to  that  of  the  mortar-discharge,  is  made  to  pass  over 
sluice-plates  from  1'  to  2^'  in  width;  hence,  the  comparatively  small 
percentage  of  amalgam  obtained  from  them.  The  only  condition  under 
which  narrower  plates  are  permissible,  is  where,  previous  to  receiving 
the  pulp,  a  certain  amount  of  the  solid  matter  has  been  diverted.  Where 
all  the  pulp  goes  from  the  plates  to  concentrators,  the  latter  become  an 
important  factor  in  regulating  the  amount  of  water  turned  into  the 
battery.  The  feed-water  required  for  concentrators  of  the  vanner  types 
is  from  one  to  two  gallons  per  minute. 

In  dressing  the  apron-plates  prior  to  starting  the  stamps,  they  are 
first  washed  down  with  the  hose,  to  remove  all  particles  of  coarse  sand 
which  might  otherwise  scratch  the  plate  during  the  subsequent  dress- 
ing, then  rubbed  with  a  brush,  using,  if  necessary,  some  fine  tailings- 
sand  to  remove  all  spots  or  stains.  During  this  part  of  the  operation, 
the  brush  is  moistened  with  difierent  chemicals,  according  to  the  prefer- 
ence of  the  millman;  some  use  weak  cyanide  of  potassium;  others  use 
strong  brine,  with  a  small  addition  of  sulphuric  acid;  also,  sal  ammoniac, 
or  soda,  or  lye,  besides  other  combinations.  In  many  cases  the.-e  pre- 
scriptions are  carefully  guarded  by  their  possessors  as  trade  secrets,  and 
are  considered  the  basis  of  all  the  success  the  owner  has  achieved  in 
his  business.  Anything  that  will  give  the  plate  a  clean  surface,  free 
from  oxidation  stains,  and  retain  for  the  quicksilver  its  bright  condition, 
is  useful  in  this  respect.  The  main  point  to  achieve  success  is  to  always 
keep  the  amalgam  on  the  plate  bright,  and  of  the  right  consistency,  and 
this  art  can  only  be  perfectly  acquired  by  actual  practice  around  the 
battery  and  plates.  After  the  plate  has  been  thoroughly  cleaned,  quick- 
silver is  thinly  sprinkled  over  the  entire  surface,  through  a  cloth,  and 
spread  evenly  by  means  of  a  brush  or  piece  of  blanket,  and  finally  the 
surface  gone  over  with  a  soft  broom  or  brush,  from  side  to  side;  this 
leaves  the  amalgam  remaining  on  the  plate  with  fine  ridges  parallel  to 
the  screen. 


CALIFORNIA   GOLD    MILL    PRACTICES. 


39 


Among  the  plate  devices  used  in  California  mills,  which  may  take  the 
place  of  the  apron-plates,  or  may  follow  them,  is  a  late  invention  known 
as  the  Gold  King  Amalgamator.  It  consists  of  an  iron  cylinder,  or  drum, 
6'  long  and  12^"  in  diameter,  divided  lengthwise  into  two  equal  parts, 
hinged  together,  and  capable  of  being  locked.  Fitting  tight  inside  of 
the  cylinder  are  two  corresponding  semi-cylindrical  silver  plates,  each 
with  two  longitudinal  ribs  set  radially,  at  one-third  distance  apart  and 
about  3"  deep.     The  upper  end  of  the  cylinder  is  furnished,  around  the 


Fig.  30.    Gold  King  Amalgamator. 

circumference,  Avith  tooth-gearing,  into  which  fits  a  spur  wheel  with  a 
four  to  one  transmission,  driven  by  a  12"  pulley.  In  the  center  of  this 
end  is  a  3"  feed  opening,  through  which  the  pulp  is  dropped  into  the 
revolving  cylinder.  A  trunnion  at  the  lower  end  rests  in  a  slide  bear- 
ing, that  permits  of  fixing  the  grade  to  be  given  the  cylinder  by  means 
of  set  screws.  The  machine  makes  forty  revolutions  per  minute,  the 
pulp  requiring  about  3^  minutes  to  pass  through  the  machine  before 
being  discharged.     It  is  run  by  less  than  i  H.P.,  and  is  easily  set  up. 


Fig.  31.    Gold  King  Amalgamator. 

The  pulp,  when  dropped  in  the  closed  cylinder,  is  caught  by  one  of  the 
ribs  and  raised  to  the  highest  point,  when  it  drops,  to  be  again  taken 
up  by  the  next  rib,  advancing  at  the  same  time  a  short  distance  ahead. 
The  discharge  is  through  the  center  at  the  lower  end  of  the  cylinder. 
From  15  to  20  tons  can  be  passed  through  in  a  day;  or  for  a  larger  sized 
machine,  from  25  to  40  tons. 

Where  concentrators  are  used  in  the  mill,  the  sluice-plates  that  follow 
the  aprons  are  usually  not  over  8'  in  length  and  from  16"  to  20"  wide. 


40  ■  CALIFORNIA   GOLD    MILL    PRACTICES. 

with  less  grade  than  the  apron.     This  latter  point  is  reversed  in  some 
mills,  and  the  sluice-plates  are  comparatively  steep. 

Between  the  aprons  and  the  sluice-boxes  a  drop  box  is  placed,  into 
which  the  pulp  from  the  aprons  discharges;  there  is  one  to  each  apron, 
or  one  for  two  adjoining  ones.  These  boxes  are  1'  wide  and  about  10" 
deep,  with  flat  or  partly  sloping  bottoms;  these  latter,  generally 
where  one  box  is  used  for  two  aprons,  the  bottoms  slojjing  from  each 
end  across  the  width  of  the  apron,  toward  a  central  part  where  the 
bottom  is  level,  and  from  whence  it  passes  by  overflow  to  the  sluice- 
plates.  These  sluice-plates  are  in  short  lengths,  and  are  either  laid  over- 
lapping or  screwed  down  to  form  a  continuous  sheet,  and  are  prepared 
and  treated  in  the  same  manner  as  the  aprons.     Of  late  years  a  useful 


Amalgam  Trap. 


addition  is  being  made  to  the  plates  in  the  form  of  a  shaking-plate,  of 
the  same  width  as  the  aprons,  and  immediately  below  them.  It  is 
either  suspended  or  on  a  movable  frame,  and  is  given  an  end  or  side- 
shaking  motion  and  light  grade;  for  an  end  shake,  the  motion  is 
imparted  by  a  cam  with  |"  stroke,  and  two  hundred  strokes  per  minute. 
The  correct  strokes  for  these  plates  must  be  determined  at  each  mill  by 
experiment.  Their  efficiency  was  demonstrated  in  one  mill,  where  the 
pulp  passed  over  two  consecutive  apron-plates,  and  then  to  the  shak- 
ing plate,  which  accumulated  a  greater  amount  of  amalgam  then  the 
second  apron. 

Amalgam  Traps  (Fig.  32). — To  retain  any  quicksilver  or  small  parti- 
cles of  amalgam  that  escape  inadvertently  while  dressing  or  cleaning 
the  plates,  traps  are  generally  placed  below  the  sluice-plates,  and  are 
made  of  various  patterns.  The  general  idea  is  for  the  pulp  to  drop  to 
the  bottom  of  a  deep  vessel  and  flow  out  at  or  near  the  upper  edge;  in 
some  cases,  passing  over  a  series  of  inclined  shelves  of  copper  plates 
during  the  descent.  A  simple  and  very  efficient  contrivance  for  an 
amalgam  trap  is  to  suspend  a  narrow  box  by  one  end  and  attach  the 
opposite  end  to  a  rod  connected  by  a  pin  to  an  eccentric,  through  which 
it  receives  a  gentle  shaking  motion  in  the  direction  of  its  long  side.  The 
tailings  are  introduced  into  a  stationary  box  immediately  above,  from 
whence,  diluted  with  fresh  water,  the  pulp  passes  over  the  top  of  a  par- 
tition in  an  even  sheet  to  the  suspended  box  below.  The  proper  motion 
for  this  lower  box  must  be  found  by  experimenting,  for  which  purpose 


CALIFORNIA    GOLD    MILL    PRACTICES.  41 

the  end  of  the  rod  is  supplied  with  a  series  of  holes,  to  shorten  or 
lengthen  the  stroke.  The  motion  should  be  just  sufficient  to  keep  the 
pulp  suspended  like  quicksand,  without  splashing  or  caking  on  the 
bottom. 

Avialgamating. — Quicksilver  is  charged  by  hand  into  the  mortars 
through  the  throat,  at  stated  intervals,  with  a  small  wooden  spoon. 
Automatic  quicksilver-feeders  have  been  invented  that  are  worked  from 
the  cam-shaft  in  such  a  manner  that,  at  stated  intervals,  a  little  cup  on 
a  ratchet  wheel,  in  revolving,  dips  quicksilver  from  a  reservoir  and 
drops  it  through  a  tube  into  the  mortar.  This  insures  absolute  regu- 
larity; but  for  some  reason  they  do  not  find  much  application  in  Cali- 
fornia. Retorted  or  new  quicksilver  should  be  used  for  charging  as 
well  as  for  dressing  the  plates.  It  is  a  good  plan  to  keep  the  quicksilver 
used  for  these  purposes  covered  with  a  weak  solution  of  cyanide  of 
potassium. 

Quantity  of  Quicksilver. — To  form  some  idea  of  the  amount  of  mercury 
necessary  to  be  introduced  when  handling  an  ore,  the  value  of  which  is 
not  known,  a  horn-spoon  test  of  a  weighed  quantity  is  made,  and  the 
quantity  of  gold  decided.  Gold  alloyed  with  an  appreciable  amount  of 
silver  requires  a  larger  addition  of  quicksilver  than  does  a  purer  gold. 
One  ounce  of  gold  of  average  fineness  can  be  amalgamated  with  1  oz.  of 
quicksilver,  but  for  a  safety  margin,  an  allowance  must  be  made,  so  that 

2  ozs.  will  answer  better;  and  with  extremely  finely  divided  gold,  2^  or 

3  ozs.  If  the  stamps  have  a  duty  of  two  tons  each,  the  amount  of  rner- 
cury  requisite  to  amalgamate  the  gold  contained  in  one  ton  of  ore 
should  be  divided  into  five  parts  and  introduced  at  half-hour  intervals. 
If  the  ore  be  of  low  grade,  the  necessary  portion  may  be  added  every 
hour;  as  the  value  increases,  the  stated  intervals  for  charging  should  be 
reduced.  The  larger  proportion  of  California  gold  ores  receive  mercury 
every  half  hour. 

The  skilled  millman  judges  from  the  condition  of  his  plates  as  to 
whether  he  is  charging  correctly.  He  places  his  finger  on  the  apron- 
plate,  and  if  the  accumulated  amalgam  gives  to  a  gentle  resistance,  and 
has  a  putty-like  feeling,  the  condition  is  about  right;  when  hard  to 
move,  he  must  increase  the  charge;  or  if  thin,  reduce  it.  The  harder 
the  amalgam,  the  more  it  assumes  a  dead-white  color.  The  matter  of 
correct  charging  of  the  mercury  requires  a  constant  watching,  as  on  this 
depends  the  success  of  battery  amalgamation ;  hence,  the  ore  should  be 
frequently  tested  with  the  horn-spoon. 

Amalgam  retained  on  the  inside  battery-plates  weighs  heavier,  for  the 
bulk,  than  the  apron  amalgam.  There  is  a  diversity  of  opinion  amonc' 
millmen  as  to  how  often  the  amalgam  accumulated  on  the  aprons  and 
sluices  should  be  removed.  Thus  it  is  found  in  the  California  milling- 
practices  that  aprons  are  scraped  as  often  as  twice  a  day  in  some  mills, 
while  in  others  it  is  allowed  to  accumulate  from  one  clean-up  day  to 
the  next,  which  sometimes  means  once  a  month.  Personal  experiments 
by  the  writer,  conducted  in  various  mills,  invariably  showed  a  yield  of 
more  amalgam  from  the  more  frequent  removal  of  the  accumulations 
but  as  the  clean-up  of  the  apron  would  require  the  cessation  of  crushinfy, 
such  frequent  stoppages  would  materially  lessen  the  output.  To  avoid 
this,  as  the  upper  18"  of  the  apron-plate  retains  about  75%  of  all  the 


42  CALIFORNIA   GOLD   MILL    PRACTICES. 

amalgam  on  it,  this  much  of  the  apron-plate  may  be  made  separate 
from  the  rest,  and  held  in  place  by  wooden  buttons  on  the  side,  so  that 
it  can  be  removed  at  any  time  while  the  battery  is  at  work,  and  an  extra 
plate,  provided  for  the  purpose,  slipped  in  its  place.  Once  or  twice  in 
the  twenty-four  hours  it  is  advisable  to  hang  up  the  stamps,  one  battery 
at  a  time,  and  dress-over  the  surface  of  the  apron-plate,  sprinkling,  if 
necessary,  a  little  fresh  mercury,  and  brushing  it  into  the  adhering 
amalgam,  after  which  the  amalgam  should  be  evenly  spread  out  again. 
This  takes  but  very  few  minutes.  Frequently,  when  dressing  a  plate, 
a  very  fine  coating  of  a  brownish  or  grayish  color  can  be  seen  adhering 
to  the  surface,  which,  on  the  application  of  the  brush,  is  easily  detached 
and  thoughtlessly  washed  off.  If  this  be  examined  under  the  glass,  it 
will  be  found  to  contain  considerable  gold,  hence  should  be  gathered 
carefully  in  the  gold-pan. 

To  remove  the  amalgam  from  the  plates,  the  stamps  are  hung  up,  the 
battery-water  shut  oflf,  and  the  front  of  the  screen  and  plates  hosed  off 
to  remove  any  sand  which  would  scratch  the  plate.  The  surface  of  the 
plate  is  softened  by  the  addition  of  quicksilver  until  the  amalgam 
moves  readily.  Then,  commencing  at  the  bottom  and  working  upward, 
with  a  piece  of  rubber,  or  rubber  belting,  4"  long  with  square  edges,  the 
amalgam  is  pushed  ahead  to  the  upper  end  of  the  apron,  gathered  in  a 
heap,  and  transferred  to  a  pan  or  bowl  by  means  of  a  scoop.  The 
amalgam  is  taken  to  the  clean-up  room  for  further  cleansing. 

Where  the  amalgam  has  been  retained  on  the  plate  for  any  length  of 
time,  as  during  an  entire  run,  it  requires  a  chisel  or  case-knife  to  remove 
it  thoroughly,  care  being  taken  not  to  scratch  the  plate.  In  scraping  a 
plate  it  is  not  advisable  to  remove  ("skin")  all  the  amalgam;  enough 
should  be  left  to  form  a  thin  coating,  when  ready  to  commence  crushing 
again. 

All  mills  experience  more  or  less  loss  of  quicksilver,  partly  through 
careless  handling  in  dressing  the  plates,  but  also  from  the  "flouring" 
of  the  mercury  (breaking  up  into  minute  globules)  after  charging  in 
the  battery.  This  loss  is  extremely  variable  in  the  different  mills, 
depending  on  the  nature  of  the  ore,  high  discharge,  and  low  tempera- 
ture of  the  battery-water.  Ores  carrying  much  talc,  black  oxide  of 
manganese,  galena,  or  arsenical  pyrites,  cause  a  good  deal  of  flouring  of 
the  mercury.  A  further  cause  of  loss  is  through  incomplete  retorting, 
a  certain  amount  of  mercury  being  retained  in  the  bullion,  which  is  vol- 
atilized in  the  subsequent  melting.  One  half  ounce  to  the  ton  of  ore 
may  be  taken  as  near  the  average  loss  for  California  mills,  although  in 
a  few  cases  these  figures  are  doubled. 

As  the  amalgam  retained  in  the  battery  is  less  liable  to  loss  than 
that  portion  adhering  to  the  outside  plates,  the  aim  of  the  millman  is 
to  retain  the  largest  proportion  inside  the  screens.  The  coarseness  of 
the  gold  has  a  good  deal  to  do  in  this  direction,  as  well  as  the  splash 
and  height  of  discharge.  In  some  mills,  as  high  as  80%  of  the  total 
yield  of  amalgam  will  be  found  in  the  battery;  it  is  always  greatest, 
with  the  same  grade  of  gold,  where  the  most  copper-plate  surface  is  found 
inside  the  battery.  The  average  proportions  of  amalgam  retained  in 
this  country  may  be  stated  as  two  thirds  in  the  battery  as  against  one 
third  on  the  (outside)  plates,  depending,  of  course,  on  the  character  of 
the  gold  in  each  district. 

As  the  proper  condition  of  the  mercury  is  a  matter  of  importance  to 


CALIFORNIA   GOLD    MILL    PRACTICES.  43 

the  millman,  it  is  well  to  become  familiar  with  its  dififerent  phases. 
Pure  mercury  is  bright,  quick,  and  does  not  change  its  appearance  on 
exposure  to  the  air  at  ordinary  temperature,  but  evaporates  slightly. 
As  the  temperature  decreases  it  becomes  stifi'er,  and  at  low  temperature 
assumes  a  more  leaden  appearance;  in  raising  the  temperature  it 
becomes  more  liquid.  At  60°  Fahr.  it  emits  vapor  sufficient  to  discolor 
a  bright  piece  of  gold  when  suspended  over  it  in  a  closed  vessel.  Pure 
mercury,  if  dropped  into  a  porcelain  dish  or  on  a  table,  will  form  into 
spherical  globules,  whereas  the  impure  metal  breaks  into  pear-shaped 
drops,  and  if  very  impure,  the  particles  drag  a  tail  when  moved.  If 
containing  lead,  a  skin  of  metal  will  remain  on  the  fingernails  when 
passing  the  hand  through  the  surface.  The  introduction  of  grease  or 
unctuous  substances,  like  clay  and  talc,  incline  the  metal  to  separate 
into  extremely  fine  globules — flouring.  Quicksilver  is  attacked  by 
heated  concentrated  sulphuric  acid,  but  is  not  affected  by  it  when 
diluted.  Muriatic  acid  likewise  does  not  affect  it.  Nitric  acid  attacks 
it  and  forms  nitrate  of  mercury,  a  white  compound.  Quicksilver  that 
has  been  used  in  gold-milling  dissolves  and  retains  a  certain  amount 
of  gold,  which  remains  with  it,  even  after  retorting.  If  quicksilver  of 
this  description  be  left  for  months  undisturbed  in  a  cold  place  and  then 
carefully  poured  or  siphoned  off,  a  network  of  fine,  needle-shaped 
crystals  of  amalgam  will  be  found  in  the  bottom  of  the  vessel,  derived 
from  this  gold  held  in  solution. 

Sodium  Amalgam. — As  sodium  amalgam  is  frequently  added  to  the 
quicksilver  by  millmen,  the  following  method  of  preparing  it  is  given: 
Dissolve  small,  dry  chips  of  clean  sodium,  freshly  cut  from  a  stick,  in 
pure,  dry  mercury,  gently  heated  in  a  flask  or  porcelain  dish;  add  it 
piece  by  piece  until  the  mass  has  attained  the  consistency  of  soft  putty, 
which  should  always  be  kept  dry  and  well  bottled,  as  it  deteriorates 
rapidly  in  the  air.  This  preparation  is  added  to  the  mercury  when 
dressing  the  plates;  and  to  know  when  the  proper  amount  has  been 
added,  dip  a  brightened  nail  into  the  quicksilver,  which  will  adhere 
slightly  to  the  edges  of  the  nail  if  the  amount  be  correct;  whereas,  if  it 
becomes  entirely  coated,  too  much  has  been  used,  and  more  quicksilver 
must  be  added;  on  the  other  hand,  if  there  be  no  signs  of  adhesion,  more 
sodium  amalgam  must  be  added. 

Nearly  all  commercial  mercury  needs  cleaning.  The  handiest  way  is 
to  digest  with  dilute  nitric  acid  for  twenty-four  hours,  taking  one  part 
of  acid  to  three  of  water.  In  retorting  foul  quicksilver  to  purify  it,  the 
retort  should  only  be  half  filled  and  the  quicksilver  covered  with  a 
layer  of  quicklime  or  charcoal  powder.  The  heating  should  then  be 
done  very  gradually,  the  retort  not  being  brought  to  a  full  red  heat. 

Cleaning  Up. — When  ready  to  clean  up  a  mortar,  the  feed  of  ore  is 
shut  off,  and  the  speed  of  the  stamps  reduced  until  as  much  of  the 
sand,  etc.,  as  possible  has  been  discharged  and  iron  strikes  on  iron. 
The  battery-water  is  then  shut  off",  the  self-feeder  pushed  back,  tlie 
stamps  hung  up,  the  splash-board  or  canvas  removed  from  in  front  of  the 
screen,  and  the  face  of  the  latter  washed  off"  with  the  hose.  The  aprons 
and  plates  are  then  scraped,  and  the  aprons,  if  fixed,  covered  with 
planks  near  the  mortar,  to  protect  them  while  working  around  the 
mortar.     The  keys  that  hold  the  screen  in  place  are  withdrawn  and  the 


44  CALIFORNIA   GOLD    MILL    PRACTICES. 

screen-frame  loosened  and  slightly  raised,  permitting  the  water  that  is 
still  retained  in  the  mortar  to  gradually  run  out;  a  too  sudden  raising 
of  the  screen-frame  from  the  chock-block  would  cause  the  water  to  escape 
in  a  body  and  possibly  wash  amalgam  from  the  plates.  After  raising 
the  screen  out  of  the  grooves,  the  chock-block  and  inside  plates  are 
removed  and  all  of  them  carefully  washed  over  the  apron,  scraped,  and 
set  to  one  side  or  removed  to  the  clean-up  room  for  treatment.  The 
sand  mixed  with  ore  on  and  around  the  dies  is  taken  out  by  trowels  and 
passed  through  some  other  mortar,  or  retained  to  place  around  the  dies 
when  returned  to  the  mortar.  The  dies  are  broken  out  of  their  beds 
with  the  help  of  chisels  and  crowbars;  when  the  center  or  end  die  has 
been  successfully  worked  loose,  the  remaining  ones  are  easily  taken  out, 
washed,  examined  for  any  adhering  amalgam  (which  is  scraped  off),  and 
placed  on  the  floor,  in  the  same  order  they  occupied  in  the  battery,  ready 
to  be  replaced.  The  remainder  of  the  material  in  the  mortar  is  then 
easily  removed,  and  placed  in  the  clean-up  barrel;  in  small  mills  it  is 
panned  in  a  water-box  provided  for  the  purpose  in  the  clean-up  room. 
In  the  revolving  clean-up  barrel,  pieces  of  quartz  or  old  iron,  with  an 
additional  amount  of  quicksilver,  are  added,  and  the  barrel  is  half 
filled  with  water,  where  it  is  left  revolving  for  a  couple  of  hours.  As 
all  battery  sands  contain  more  or  less  nails  and  chips  of  iron  and  steel, 
these  are  removed  by  a  magnet  while  panning  out.  The  clean-up  barrel 
is  discharged  through  a  manhole  into  a  bucket  placed  over  a  rifiled 
sluice.  The  bulk  of  the  quicksilver  and  amalgam  is  retained  in  the 
bucket,  and  the  overflow  passes  into  the  sluice. 

After  all  the  sand,  etc.,  has  been  removed  from  the  battery,  the  inside 
is  washed  out,  and  any  amalgam  found  adhering  to  the  sides  or  linings 
is  carefully  scraped  off  with  a  case-knife  and  placed  with  the  rest  of  the 
amalgam  for  further  cleaning.  A  bed  of  dry  tailings-sand  is  then  spread 
over  the  bottom  of  the  mortar,  and  the  dies  replaced  exactly  as  they  were 
before.  The  tappets  are  then  set,  plates  and  screens  put  in,  the  feeder 
replaced,  water  turned  on,  and  the  battery  once  more  started. 

The  operation  of  cleaning-up  the  batteries  is  performed  usually  once 
or  twice  a  month,  and  in  some  mills  once  a  week,  at  which  time  tappets 
are  re-set  and  any  necessary  repairs  made;  also,  any  shoes  that  are  too 
thin  or  broken  are  knocked  from  the  boss  and  new  ones  substituted. 
As  one  new  shoe  in  a  battery  of  old  ones  causes  irregular  working,  it 
is  best  to  replace  all  the  shoes  at  the  same  time,  and  if  any  of  them 
are  not  worn  down  thin  enough  to  discard,  they  may  be  set  aside  and 
used  to  replace  a  broken  one  at  some  future  time.  The  same  thing  holds 
good  with  the  dies,  for  if  they  are  of  uneven  height  they  interfere  with 
the  regularity  of  "  splash, "  and  the  higher  die  will  be  pounding  iron 
while  the  remainder  have  still  a  sufficient  cushion  of  quartz. 

The  amalgam  obtained  from  a  clean-up  is  washed  in  small  batches 
in  the  gold-pan,  to  free  it  from  all  sand,  fine  iron,  or  sulphurets,  and 
then  stirred  up  with  an  excess  of  mercury  in  a  wedgewood  mortar, 
bringing  all  impurities  to  the  surface;  this  dross  is  skimmed  ofi'  and 
collected  for  further  cleaning.  The  superfluous  quicksilver  is  squeezed 
through  a  straining  cloth  or  closely  woven  drilling,  or  through  buck- 
skin, and  the  resulting  balls  of  amalgam  retorted.  This  squeezing  is 
best  done  by  hand.  After  first  thoroughly  wetting  the  cloth  or  skin, 
it  is  laid  loosely  over  a  cup  or  bowl,  and  a  convenient  amount  of  amal- 
gam poured  in  the  center,  enough  to  make,  when  squeezed,  a  ball  of  20 


CALIFORNIA   GOLD    MILL    PRACTICES 


45 


«55:j^^ 


Fig.  33. 


Fig.  34. 


46  CALIFORNIA   GOLD    MILL    PRACTICES.  I 

to  30  ozs.  The  ends  of  the  cloth  are  then  gathered  tightly  together,  and 
commencing  near  the  ends,  it  is  twisted  until  the  amalgam  is  compressed 
to  a  hard  ball,  the  strained  quicksilver  dropping  into  a  pan  of  water 
beneath.  It  is  not  good  practice  to  squeeze  the  balls  too  dry,  as  the  last 
quicksilver  expressed  is  heavily  saturated  with  gold. 

In  large  mills  the  retorting  is  done  in  pans  placed  in  an  iron  cylin- 
drical retort  built  into  a  furnace,  where  the  flame  passes  under  and 
around  it.  (See  Figs.  33  and  34.)  But  in  the  majority  of  cases  in 
California  they  use  the  cup-shaped  iron  retort.     (See  Fig.  35.)     These 

FLATTOP  RETOffT. 


DOAf£  TOP  ff£TOPT. 


Fig.  35. 

are  made  in  different  sizes,  numbered  from  1  to  7;  No.  1  containing 
150  ozs.,  and  No.  7,  2,000  ozs.  They  are  made  of  cast-iron,  with  flat  or 
half-spherical  lids,  which  are  secured  to  the  retort  by  clamps  and  wedges 
or  thumb-screws,  the  flanges  being  ground  together.  From  a  vent-hole 
in  the  cover  a  curved  condensing-pipe,  securely  screwed  in,  extends 
several  feet.  The  retort  is  placed  in  a  ring-standard,  or  suspended  when 
retorting,  and  should  always  have  a  space  of  about  6"  beneath  it.  In 
preparing  to  retort,  the  inside  is  well  rubbed  with  chalk  and  the  balls 
of  amalgam  broken  up  and  dropped  in  loosely;  not  pressed  down  into  a 
solid  cake,  as  is  sometimes  the  practice,  as  that  retards  the  operation. 
The  flanges  of  the  retort  and  lid  are  then  luted  together  with  a  thin 
paste  of  flour  and  water  or  sifted  wood  ashes  and  water  (the  former  is 
preferable),  and  securely  fastened.  The  extended  end  of  the  condens 
ing-pipe  is  j^laced  in  a  vessel  with  water,  and  as  this  pipe  must  be  kept 
cool,  fresh  water  is  kept  passing  over  it  during  the  entire  operation. 
Tlie  retort  should  never  be  filled  to  its  full  capacity,  to  avoid  danger  of 
an  explosion  through  the  amalgam  swelling  and  closing  the  vent.  At 
first  a  light  fire  should  be  started  at  the  top,  and  the  heat  gradually 
increased  until  drops  of  quicksilver  issue  from  the  end  of  the  condensing- 
pipe.  The  retort  should  then  be  kept  at  a  red  heat  until  no  more  quick- 
silver is  seen  to  issue  from  the  pipe,  when  the  temperature  should  be 
raised  to  a  bright  "  cherry  heat"  for  a  short  time.  The  retort  should 
be  kept  covered  by  the  fire  during  the  whole  operation.     If  during  the 


CALIFORNIA   GOLD    MILL    PRACTICES.  47 

retorting  the  condensing-pipe  should  suck  water,  it  should  be  raised 
momentarily  out  of  the  water  to  permit  of  the  latter  flowing  out.  A 
better  arrangement,  and  one  that  obviates  this  difficulty,  is  to  attach 
firmly  to  the  end  of  the  pipe,  a  rubber  or  canvas  bag  in  the  water,  which 
will  distend  itself  as  soon  as  the  mercury  commences  to  flow,  and  col- 
lapse when  the  distillation  ceases.  When  the  operation  is  completed, 
which  usually  occupies  about  two  hours,  if  the  amount  be  not  very 
large,  the  quicksilver  is  removed  and  the  retort  taken  from  the  fire  and 
allowed  to  cool;  the  lid  is  removed  and  the  retort  turned  over  a  dry 
gold-pan.  If  the  gold  adheres  to  the  retort,  a  few  taps  with  the  hammer 
on  the  bottom  or  the  help  of  a  long-handled  chisel  will  release  it. 
Well-cleaned  and  retorted  amalgam  should  show  a  good  yellow  color. 
If  black  spots  be  seen  it  is  proof  that  the  cleaning  was  not  thoroughly 
done,  and  a  pale-whitish  color  shows  that  it  still  contains  quicksilver. 
Care  should  be  observed,  when  removing  the  lid  of  the  retort,  to  avoid 
inhaling  any  fumes  retained  therein.  All  retorted  amalgam  should  be 
melted  and  run  into  a  bar,  before  shipping,  as  it  saves  losses  incurred 
by  abrasion  where  the  distance  is  great  to  the  shipping  point.  The 
melting  is  performed  in  a  black-lead  crucible,  which,  when  new,  must 
first  be  dried  and  annealed  by  placing  the  inverted  crucible  and  lid  in 
the  furnace  with  a  slow  fire,  which  is  gradually  increased  until  the 
crucible  is  red  hot.  When  ready  to  commence  melting,  the  crucible  is 
placed  on  a  firebrick  in  the  furnace,  after  introducing  the  retorted  bullion, 
in  not  too  large  pieces,  with  borax,  and  covered  with  the  lid,  adding,  if 
necessary,  more  of  the  bullion  as  the  metal  subsides.  After  all  is 
melted  down,  the  slag  is  skimmed  off  carefully  from  the  top  of  the  metal, 
which  should  show  a  bright  surface.  It  is  then  ready  for  pouring. 
Should  the  surface  not  appear  bright,  but  show  a  scum  on  top,  some 
lumps  of  borax  must  be  added,  the  crucible  again  covered  and  heated, 
when  the  scum  will  be  slagged  and  skimmed  as  before,  when  it  is  ready 
to  be  poured  into  a  mould.  Should  the  second  addition  of  borax  fail 
to  produce  a  bright  surface,  a  very  little  niter  may  be  added  with  the 
borax.  Before  using  the  mould  it  should  be  warmed  and  smoked  on 
the  inside  by  holding  over  the  flame  of  a  lamp  or  over  a  dish  with  burn- 
ing rosin.  The  metal  in  the  pot  should  be  stirred  before  pouring;  the 
stirrer,  an  iron  rod,  must  be  heated  before  introducing  it.  The  bar, 
when  solid,  is  turned  out  of  the  mould,  and  any  adhering  slag  is  ham- 
mered ofl';  it  can  then  be  dipped  into  water  to  thoroughly  cool  it,  dried, 
and  weighed.  Two  small  chips  should  then  be  taken — one  from  an 
upper  corner,  the  other  from  the  diagonally  opposite  lower  corner — to 
be  assayed. 

ASSAYING    AND    SAMPLING. 

Although  at  present  most  California  mills  have  their  own  assayers  to 
test  the  ore  and  the  tailings,  the  time  was  not  so  very  remote  when  it 
was  not  considered  requisite  to  do  any  assaying.  The  expert  millman 
could  tell  (?)  by  horn-spoon  test  how  much  his  ore  would  mill  to  the 
ton;  and  if  a  horn-spoon  test  of  the  tailings  showed  no  amalgam,  he 
confidently  asserted  that  all  was  being  saved.  It  was  decidedly  a  case 
where  "ignorance  was  bliss."  No  gold  milling  can  be  carried  on  under- 
standingly  without  light  being  thrown  on  the  different  results  achieved, 
and  which  can  only  be  given  by  careful  sampling  and  assaying.  It  is 
not  sufficient  to  know  that  a  certain  loss  has  been  sustained.     It  should 


48  CALIFORNIA   GOLD    MILL    PRACTICES. 

be  accompanied  by  a  knowledge  in  what  particular  part  of  the  opera- 
tion the  loss  has  been  incurred,  to  enable  the  operator  to  remedy  the 
evil;  hence,  the  necessity  of  constant  sampling  and  assaying.  In  some 
cases  the  loss  will  be  found  entirely  in  the  coarse  sands,  indicating  that 
the  screens  are  not  fine  enough;  again,  the  loss  may  be  entirely  through 
sliming  of  the  ore,  or  the  missing  percentages  of  gold  will  be  found 
mostly  in  the  sulphurets.  The  assay  test  alone,  with  correct  sampling^ 
furnishes  the  knowledge. 

Sampling. — Samples  should  be  taken  regularly  of  the  ore  as  it  comes 
to  the  mill,  as  well  as  of  the  tailings  as  they  pass  off,  for  without  the 
knowledge  derived  from  these  two  operations  there  is  no  means  of  con- 
trolling the  work. 

Ore,  as  it  arrives  at  the  mill,  is  sampled  by  taking  a  stated  amount 
(shovelful)  from  each  ore-car  or  wagon,  and  throwing  the  samples 
together  in  a  pile  on  a  clean-swept  floor  or  into  a  small  bin.  The  pile 
should  be  shoveled  over  after  breaking  the  pieces  to  the  size  of  macadam; 
or  if  the  pile  be  too  large,  cut  through  it  at  right  angles,  throwing  the 
rock  from  the  trench  thus  made  in  a  pile  by  itself.  This  should  be 
crashed  or  broken  to  a  nearly  uniform  size,  mixed  by  shoveling,  and 
made  into  a  low,  truncated  cone,  which  is  divided  into  four  equal  parts 
by  making  a  cross  on  the  surface,  and  throwing  out  two  diagonal  quar- 
ters, which  are  again  reduced  in  size,  made  into  a  second  similar  cone, 
and  treated  as  before.  This  quartering  and  crushing  is  continued  until 
a  half-pound  sample  is  obtained  for  fire  assay.  Great  care  must  be 
observed  when  removing  the  different  quarters  to  see  that  all  the  fine 
dust  is  swept  up  and  added  to  the  pile  each  time,  as  otherwise  very  de- 
fective results  will  be  obtained.  The  rest  of  the  ore  is  returned  to  the 
main  ore-bin.  Samples  taken  in  this  way  from  the  aprons  of  the  self- 
feeders  are  likely  to  give  a  more  correct  average,  having  been  crushed, 
and  the  coarse  and  fine  dvily  mixed.  Samples  should  be  taken  at  regular 
intervals  from  the  pulp  with  the  water  that  has  passed  over  all  the 
plates,  and  also  from  the  concentrators. 

Tailings  samples  should  be  taken  at  stated  intervals  by  passing  a 
vessel  across  the  entire  width  of  the  discharge,  where  they  leave  the 
mill,  without  permitting  any  to  flow  over,  and  gathering  at  each  interval 
an  even  amount.  This  is  allowed  to  settle  in  a  bucket  and  the  clear 
water  then  poured  off"  carefully  or  drawn  off'  with  a  siphon.  The  residue 
is  dried  and  thoroughly  mixed,  and  several  packages  of  5,000  to  10,000 
grains  each  weighed  out.  In  some  mills  tailings  samples  are  obtained 
automatically,  using  their  current  as  the  motive  power  for  the  sampler, 
which  works  by  intermittently  deflecting  a  spout  through  the  tailings 
where  they  finally  drop  from  the  sluices,  obtaining  the  sample  across 
the  entire  section  of  the  current.  An  appliance  for  this  purpose  is 
shown  in  the  accompanying  drawing.     (Fig.  36.) 

To  ascertain  the  amount  of  slimes  in  the  tailings  sample,  put  one  of 
the  packages  into  a  bucket,  add  water,  and  stir  it.  After  settling  two  or 
three  minutes,  pour  off  the  muddy  water  into  a  separate  vessel;  repeat 
this  operation  until  the  water  comes  off"  clear;  add  a  little  powdered 
alum  in  the  vessel  containing  the  muddy  water,  and  when  the  mud  has 
all  settled,  draw  off"  the  top  water  carefully  and  evaporate  the  remainder. 
Dry  the  washed  sands  of  the  sample,  and  pass  through  difl'erent  sized 


CALIFORNIA    GOLD    MILL    PRACTICES. 


49 


screens,  weighing  the  difierent  amounts  as  they  have  passed,  and  assay 
each  size;  this  will  show  where  the  greatest  loss  is  sustained. 

To  ascertain  where  the  loss  in  sulphurets  occurs,  it  is  sufficient  to  pass 
one  of  the  10,000  grains  samples  through  a  60-mesh  wire  screen;  weigh 
that  which  passes  through  and  that  which  remains  on  the  screen,  and 


pan  out  each  lot  carefully  by  itself,  from  one  pan  into  another,  as  long 
as  sulphurets  can  be  recovered;  then  weigh  each  batch  of  sulphurets 
separately. 

The  use  of  10,000  grains  is  recommended,  as  every  100  grains  is  1%, 
and  each  grain  is  y^ij  of  1%;  it  is  also  a  convenient  size  for  obtaining 
accurate  results.  By  using  pulp  samples  instead  of  tailings,  the  amount 
of  sulphurets  in  the  ore  may  be  ascertained. 

If  the  sulphurets  assay  $75  per  ton,  and  the  quantity  per  ton  is  1.7%, 

4 — GMP 


50  CALIFORNIA   aOLD    MILL    PRACTICES. 

the  value  of  the  sulphurets  in  one  ton  of  ore  is  found  by  multiplying 
$75  by  0.017,  which  would  be  $1  27  per  ton.  If  the  loss  of  sulphurets 
in  the  tailings  is  11  grains  out  of  the  10,000  grains  sample,  and  the 
value  of  the  sulphurets  is  $75  per  ton,  then  multiply  $75  by  0.0011,  and 
the  value  of  sulphurets  in  the  tailings  is  found  to  be  $0.0825  (8i  cents) 
per  ton  of  tailings. 

MILL    ASSAYS. 

Amalgamation  (Free-Gold)  Assay. — Take  two  pounds  (being  exactly 
one  thousandth  part  of  a  ton)  of  ore,  crush  in  an  iron  mortar,  and  pass 
through  a  No.  60  sieve;  remove  the  gold  and  other  metallic  substances 
left  on  the  sieve,  and  place  in  a  small  porcelain  dish  containing  a  little 
dilute  nitric  acid,  to  remove  any  adhering  crusts  of  oxide  of  iron,  etc., 
which  might  prevent  amalgamation;  these  residues  are  then  carefully 
washed  and  thrown  into  the  sifted  ore,  which  is  then  placed  in  a  wedge- 
wood-ware  mortar  and  mixed  with  enough  warm  water  to  make  a  stiff 
paste.  To  an  ounce  Troy  (480  grains)  of  new,  clean  mercury, /ree /rom 
gold,  add  a  piece  of  clean  sodium  about  the  size  of  a  pea.  The  mercury 
thus  highly  charged  with  sodium  is  then  thrown  into  the  mortar  con- 
taining the  sample,  and  the  mass  ground  constantly  for  an  hour,  when 
amalgamation  should  be  quite  complete.  The  mass  is  then  transferred 
to  a  gold-pan  and  carefully  Avashed  over  another  pan  or  tub,  in  which 
the  tailings  are  caught,  and  re-washed  to  save  anything  which  may 
have  escaped.  The  mercury  is  collected  and  transferred  to  a  small 
dish;  if  it  be  much  floured  and  refuse  to  run  into  globules,  stir  it  with 
a  small  piece  of  sodium  held  in  the  end  of  a  glass  tube,  which  will 
cause  it  to  run  together.  The  mercury  is  then  washed  carefully  in  clear 
water  and  dried  with  blotting  paper.  It  is  then  re-weighed,  and  if  the 
loss  exceeds  5%  the  assay  must  be  rejected  and  a  new  one  made.  The 
mercury  is  next  transferred  to  a  small  annealing-cup  or  crucible,  which 
has  been  carefully  black-leaded  inside,  covered  with  a  porcelain  or  clay 
cover,  and  volatilized  with  a  gentle  heat.  When  all  the  mercury  has 
been  volatilized,  about  50  grains  of  assay  lead  are  thrown  into  the  cruci- 
ble and  melted,  giving  it  a  rotary  motion  while  in  a  molten  state.  It 
is  then  removed,  cupelled,  and  the  "button"  weighed.  It  may  be  as- 
sumed without  sensible  error  that  the  mercury  lost  in  the  operation 
carried  the  same  proportion  of  gold  as  is  contained  in  the  mercury 
recovered;  hence  the  gold  contents  of  the  ore  will  be  found  by  multiply- 
ing the  weight  of  the  "  button  "  obtained  by  the  weight  of  the  original 
quantity  of  mercury,  and  dividing  the  product  by  the  difference  between 
the  weight  of  the  mercury  recovered  and  the  "button."  This  figure, 
multiplied  by  1,000,  gives  the  weight,  in  grains,  of  the  free  gold  and  silver 
per  ton  of  ore,  which,  for  all  practical  purposes,  may  be  assumed  to  be 
all  gold.  Should,  however,  greater  accuracy  be  desired,  hammer  the 
"button"  fiat  and  thin,  and  dissolve  the  silver  from  it  with  nitric  acid, 
and  weigh  the  gold.     The  difference  in  weight  represents  the  silver. 

Panning  Assay. — Take  2  lbs.  of  ore,  crush,  and  pass  through  a  No.  40 
sieve;  any  gold  in  the  residue  left  on  the  sieve  being  set  aside.  The 
sample  is  then  carefully  panned,  and  the  tailings  re-panned,  to  make 
sure  nothing  is  lost.  This  operation  will  show  at  once  whether  the  ore 
is  rich  in  sulphurets  or  not,  and  the  nature  of  them.  The  visible  gold 
should  be  panned  as  free  as  possible  from  all  the  sulphurets,  taking  care 


CALIFORNIA   GOLD    MILL    PRACTICES. 


51 


that  none  is  lost.  The  pan  and  its  contents,  together  with  the  residue 
left  on  the  sieve,  are  dried  by  holding  over  a  fire;  the  contents  are 
brushed  into  a  cone  of  lead-foil,  rolled  up,  melted,  and  cupelled.  The 
"  button  "  is  weighed,  and  the  free  gold  determined  by  multiplying  its 
weight  by  1,000. 

The  tailings  produced  in  the  panning  operations  should  be  panned 
over  several  times  to  collect  all  the  sulphurets,  which  should  then  be 
dried,  weighed,  and  their  percentage  in  the  ore  determined. 

Another  method  consists  in  not  separating  the  free  gold  from  the  sul- 
phurets, but  in  treating  them  both  together  by  fire-assay,  and  determin- 


FiG.  36«.    The  Hendy  Concentrator. 

ing  the  total  value  of  the  gold  present  in  them.  The  operations,  as  far 
as  described,  are  all  that  can  be  properly  considered  as  coming  under 
the  term  of  battery  amalgamation  as  practiced  in  California,  if  we  except 
the  use  of  the  riffle  and  blanket  sluices;  these  are  placed  below  all  the 
plates,  and  receive  a  very  spasmodic  attention  in  the  majorit}'  of  mills. 
Blankets  are  laid  in  strips,  about  16"  wide  and  about  6'  long,  overlap- 
ping each  other  in  double  sets  of  sluices,  set  on  a  grade  of  about  f "  to 
the  foot,  washed  in  a  separate  water-box.  The  material  thus  obtained, 
with  the  contents  of  the  riffles,  is  deprived  of  its  valuable  contents  by 
the  aid  of  arrastras,  pans,  or  Chili  mills.  But  few  blanket-sluices  are 
found  to-day  in  California  mills. 

On  the  practical  development  of  the  Plattner  chlorination  process, 
by  Mr.  Deetken,  in  the  "sixties,"  it  was  demonstrated  that  many  of  the 
low-grade  quartz  veins  carried  enough  gold  in  their  sulphurets  to  make 
their  working  profitable,  causing  attention  to  be  directed  to  the  con- 
centration of  these  ores  by  mechanical  contrivances.  From  the  constant 
and  successful  use  of  the  gold-pan  the  mechanical  application  of  a 
similar  motion  was  sought,  resulting  in  the  use  of  the  Hendy  and 
similar  concentrating  machines. 

The  Hend}'^  concentrator  consists  briefly  of  a  shallow  iron  pan  with 
an  annular  groove  on  the  outer  edge  and  a  waste  discharge  in  the  center. 
It  is  supported  on  a  central  upright  shaft  passing  through  the  center  of 
the  pan,  on  which  revolves,  above  the  pan,  a  central  bowl  to  receive  the 


52 


CALIFORNIA   GOLD    MILL    PRACTICES. 


pulp,  having  two  tubular  arms  extending  close  to  the  outer  edge  of  the 
pan;  these  uniformly  discharge  the  pulp  at  right  angles  from  their 
axis.  At  a  point  on  its  circumference  the  pan  is  attached  to  a  crank- 
shaft, making  about  220  revolutions  per  minute.  The  sulphurets  and 
small  balls  of  amalgam  gather  in  the  groove  at  the  outer  edge,  from 
whence  they  are  drawn  through  a  gate,  which  is  regulated  to  be  auto- 
matic in  its  discharge.  This  gate  is  not  opened  until  the  groove  is 
pretty  well  filled  with  sulphurets.  Two  of  these  machines,  driven  by 
one  shaft,  are  required  for  a  five-stamp  battery.  The  machine  needs 
constant  attention;  one  man  can  attend  to  twelve  machines  on  a  shift. 
They  have  been  mostly  displaced  by  the  endless-belt  machines  which 
have  developed  from  the  endless  blanket  and  shaking-table. 

In  1867  the  first  patents  for  the  revolving  belt  were  issued.*     This 
was  the  commencement  of  the  belt  concentrators,  of  which  at  jiresent 


Fig.  37.    The  Frue  Concentrator. 

the  Frue,  Triumph,  Woodbury,  Tulloch,  Embrey,  and  Johnston  are  rep- 
resentatives. To  produce  the  best  results  on  these  machines,  all  the 
stuff  should  be  sized. 


The  Frue  Vanner  (Fig.  37),  which  has  the  largest  representation  in 
California  gold  mills,  has  been  frequently  described. f  It  has  a  side 
shake  of  1",  with  from  180  to  200  strokes  per  minute,  the  belt  traveling 
upward  on  an  incline  from  3'  to  12'  per  minute.  The  belt  is  made  in 
two  sizes,  4'  and  6'  wide,  and  in  the  latest  patterns  as  made  at  the  Union 
Iron  Works,  San  Francisco,  has  practical  arrangement  for  easily  chang- 

*  From  the  records  of  the  United  States  Patent  Office. 

No.  61,426,  January  22,  1867.  T.  D.  &  W.  A.  Hedger,  Meadow  Lake,  California.  "  Revolv- 
ing sluice  for  saving  metals." 

*  *  *  "The  endless  apron  is  made  of  fabric  sufficiently  coarse  to  retain  the  heavier 
particles  which  it  receives  from  the  feed  spout,  beneath  which  issues  a  stream  of  water." 
*    *    * 

Claim  3.  *  *  *"  Separating  the  ore  by  passing  the  valuable  portion  up  the  incline 
and  the  debris  down  to  the  foot,  as  waste  matter,  as  described."    *    *    * 

No.  66,499,  July  9,  1867.  George  Johnston  and  Edwin  G.  Smith,  Auburn,  California. 
'Amalgamator  and  concentrator." 

*  *  *  "The  pulverized  ore  or  tailings  passes  to  an  endless  traveling  and  shaking 
canvas  belt,  which  ascends  against  a  stream,  carrying  the  heavier  particles  to  be  dis- 
charged into  a  box,  while  the  lighter  ones  are  carried  off."    *    *    * 

Claim  1.  The  revolving  belt  or  apron  (F),  with  its  raised  edges  (O),  having  a  shaking 
or  rocking  motion  from  side  to  side,  substantially  as  used  for  the  purpose  herein  de- 
scribed. 

No.  239,091,  March  22, 1881.    Judson  J.  Embrey,  Fredericksburg,  Va.  "Ore  concentrator." 

+  See  Vlth  Eeport  of  State  Mineralogist,  p.  92,  article  on  Concentration,  bv  J.  N.  Adams, 
E.M.;  and  Vlllth  Report,  p.  718,  "Milling of  Gold  Ores,"  by  J.  H.  Hammond,  E.M. 


CALIFORNIA   GOLD    MILL    PRACTICES.  53 

ing  the  slope  at  the  upper  end.  The  frames  of  these  modern  styles  are 
made  of  iron  instead  of  wood.  The  pulp  is  discharged  very  evenly  over 
the  belt  from  a  distributor  near  the  upper  end,  just  below  the  point 
where  clear  water  is  discharged  in  fine  jets  across  the  belt.  In  placing 
the  machine,  attention  must  be  given  to  the  solidity  of  the  frame,  and 
that  a  perfect  level  be  obtained  across  the  belt;  further,  the  pulp  and  clear 
water  must  be  distributed  in  an  even  depth  of  about  i";  the  grade  and 
upper  travel  depend  on  the  fineness  of  the  pulp,  and  must  be  regulated 
accordingly. 

The  following  guide  for  a  proper  condition  of  the  work  on  the  belt  is 
given  by  Henrv  Louis,  E.M.,  F.G.S.,  etc.,  in  his  verv  useful  work,  "A 
Handbook  of  Gold  Milling,"  1894,  p.  324:  "The  working  conditions 
should  be  so  adjusted  that  a  small  triangular  patch  of  sand  should 
show  at  each  of  the  lower  corners  of  the  belt.  These  sand-corners 
should  not  be  too  large,  but  must  be  well  marked,  and  the  two  should 
be  of  equal  size.  Should  they  be  unequal  the  fault  will  be  found  to  be 
either  in  that  the  belt  is  not  accurately  level  across,  that  the  distributor 


Fig.  38.    The  Improved  TrujMI'H  Concentrator. 

is  not  doing  its  work  properly,  or  that  some  of  the  working  parts  have 
not  been  properly  tightened  up,  so  that  there  are  other  motions  than  the 
normal  ones  communicated  to  the  belts.  Too  large  a  corner  of  sand 
shows  that  the  pulp  is  too  thick,  while  absence  of  any  corner  indicates 
that  it  carries  too  much  water." 

Two  of  the  4'  belt  vanners,  or  one  of  the  6',  handle  the  pulp  from  a 
five-stamp  battery.  The  amount  of  clear  water  required  to  be  added  is 
about  ^  cu.  ft,  per  minute;  the  vanner  requires  about  ^  H.  P 

The  Triumph  diflers  from  the  Frue,  principally,  in  that  it  has  an  end 
shake  of  1"  and  slightly  quicker  stroke  (230  per  minute),  the  bell 
making  a  forward  movement  of  3'  to  4'  per  minute.  It  receives  the 
pulp  in  a  bowl  containing  quicksilver  before  reaching  the  distributor, 
which  is  all  kept  in  agitation  by  revolving  stirrers. 

The  Woodbury  is  similar  to  the  Triumph  in  extent  and  number  of 
motions,  but  divides  the  belt  into  seven  longitudinal  partitions;  an  in- 
creased output  being  claimed  for  this  construction. 

The  Tulloch  gives  a  rocking  motion  from  a  fulcrum  on  the  floor,  making 
140  shakes  of  If"  per  minute,  using  either  canvas  or  rubber  belt.  This 
machine,  it  is  claimed,  saves  a  somewhat  larger  amount  of  the  finer  and 
richer  grade  of  sulphurets  as  compared  with  the  former  tj'pes- 


54 


CALIFORNIA    GOLD    MILL    PRACTICES. 


The  Emhrey  is  similar  to  the  Frue,  but  with  end  shake. 

The  Johnston,  with  improvements,  and  the  latest  of  the  belt  concen- 
trators placed  on  the  market,  claims  many  points  of  advantage.  It  is 
suspended  from  four  non-parallel  hangers  capable  of  adjustment,  by 
which  the  angle  of  oscillation  can  be  changed  as  required,  preventing 
the  accumulation  of  sand  at  the  edges,  such  as  occurs  with  the  hori- 
zontal side-shake  machines,  or  the  piling  of  the  sands  in  the  center  of 
the  belt,  that  occurs  with  the  rocking  motion.  The  motion  imparted  to 
this  belt  resembles  more  nearly  that  of  the  batea  than  that  of  any  of  the 
other  concentrators.  The  belt  is  made  of  No.  6  duck,  oiled  and  painted, 
but  a  rubber  belt  can  be  used  at  one  third  the  cost  of  those  with  molded 
edges,  which  are  short-lived.  Small,  hollow,  brass,  side-rollers  on  the 
shaking-frame,  form  the  raised  edges  by  curving  the  flat  belt  slightly 
upwards.     The  pulp  is  delivered  from  five  slots  running  parallel  with 


Fig.  39.    The  Johmston  Concentrator. 

the  belt  frames,  ^"  wide  and  16"  long,  leaving  10"  spaces,  into  which 
the  pulp  is  thrown  when  it  strikes  the  belt.  Here  the  separation  at 
once  takes  place;  the  sulphurets  settling  on  the  belt  are  carried  by  it 
up  to  the  clear  water,  while  the  sands  are  carried  down  the  belt.  In 
neither  case  are  the  sands  or  sulphurets  obstructed  by  the  falling  of 
water  and  sands,  as  in  other  machines  where  the  pulp  is  discharged 
across  the  belt.  The  clear  water  at  the  head  of  the  table,  instead  of 
being  discharged  from  a  stationary  box  to  the  moving  table,  is  dis- 
charged fi'om  a  distributor,  which  is  attached  to  and  moves  with  the 
table,  thus  stripping  the  belt  of  the  smallest  possible  portion  of  sul- 
phurets. Two  widths  of  belt,  54"  and  72",  are  used,  which  are  given  a 
grade  of  Y'  ^o  i"  to  the  foot,  making  about  118  side-shakes  per  minute. 
One  machine  handles  the  pulp  from  a  five-stamp  battery. 

Another  vanner,  soon  to  be  placed  before  the  mining  public,  consists 
of  the  essential  features  of  the  vanner,  but  carries  a  rubber  belt  with 
depressions  all  over  it,  2"  in  diameter  and  -g"  deep,  shaped  after  the 
batea,  while  the  entire  belt  receives  a  motion  corresponding  to  that 
given  to  a  batea. 

As  the  motion  and  grade  given  to  any  of  these  machines  can  only  be 
correct  for  a  certain  size  of  grain  in  the  pulp,  it  would  be  advisable  to 
introduce  some  method  of  sizing  the  pulp  previous  to  bringing  it  on  the 


CALIFORNIA    GOLD    MILL    PRACTICES.  55 

concentrator,  and  feeding  the  sized  material  to  different  machines.  The 
finer  the  screen  that  has  been  used  in  the  battery,  however,  the  less  does 
the  lack  of  sizing  affect  the  product  from  the  concentrators.  The  con- 
centrators should  always,  where  possible,  be  attached  to  power  inde- 
pendent from  the  stamps,  and  be  placed  on  a  floor  below  the  aprons  and 
in  a  position  to  permit  the  attendant  to  pass  all  around  and  to  con- 
veniently transport  the  concentrated  stuff  to  the  covered  drying  floor, 
which  should  be  made  with  a  slight  incline,  preferably  of  concrete,  and 
exposed  to  the  sunlight. 

Canvas  Platforms  or  Tables. — Investigation  proving  that  the  slimes 
passing  off  with  the  waste  from  the  mill  and  concentrators  still  carried 
an  appreciable  amount  of  precious  metal,  millmen  during  the  last  few 
years  have  extended  their  operations,  and  re-treat  the  hitherto  escaping 
slimes.  This  is  done  by  conveying  all  the  waste  material  from  the 
mill,  through  sluices,  to  canvas  platforms  having  the  following  general 
features.  (See  illustrations  in  chapter  on  "Typical  Mills,"  pp.  66,  69, 
and  75.) 

A  platform  is  built  of  clear,  seasoned,  and  planed,  1^"  planking,  on  a 
solid,  level  foundation,  and  given  a  grade  of  about  |"  to  the  foot,  over 
which  No.  6  canvas  is  stretched  smooth,  longitudinally,  though  some- 
times crosswise,  with  a  2"  overlap.  Particular  attention  must  be  paid 
that  the  canvas  is  stretched  smoothly  and  evenly  and  that  no  crack 
opens  between  the  planks  constituting  the  platform.  The  length  and 
width  of  the  platform  required,  depends  on  the  amount  of  pulp  to  be 
handled;  overcrowding  must  be  avoided.  The  platform  is  divided  longi- 
tudinally into  sections  corresponding  to  the  width  of  the  canvas,  which 
is  22";  the  partition  is  made  of  wooden  strips,  2"  wide  and  ^"  high, 
covering  1"  on  the  edge  of  two  adjoining  pieces  of  canvas.  Running 
along  the  head  of  the  platform  are  two  sluices,  one  placed  above  the 
other;  one  containing  clear  water,  the  other  pulp  from  the  mill,  both 
furnished  with  |"  to  1"  plug-holes  over  each  section.  Below  the  lower 
edge  of  the  platform  are  two  sluices  placed  side  by  side,  the  inside  one 
to  convey  the  waste,  the  outer  one  for  the  concentrates  (sweepings) 
from  the  platform.  When  ready  for  operation,  the  plugs  are  withdrawn, 
and  both  pulp  and  clear  water  commingled  flow  down  in  an  even  cur- 
rent and  are  discharged  through  the  bottom  waste  sluice.  After  one 
hour  or  less,  the  plug  is  inserted  in  the  pulp-box  over  the  first  section, 
and  the  clear  water  permitted  to  run  for  a  few  minutes  longer,  during 
which  time  quartz  sand  may  be  observed  passing  off  the  canvas,  leaving 
a  dark,  partly  metallic-appearing  sediment  on  the  canvas.  A  tray  or 
board  is  then  placed  over  the  waste  sluice,  connecting  the  lower  edge  of 
the  section  with  the  outside  sluice,  and  the  sediment  is  removed  from 
the  canvas,  either  by  sweeping  or  with  the  aid  of  a  hose  with  a  flattened 
nozzle,  to  be  worked  later  by  chlorination  or  cyanide  process. 

The  following  is  a  description  of  an  improved  canvas  plant  erected 
and  operated  in  Amador  County,  by  the  patentee,  Mr.  Gates.  In  this 
case,  the  pulp  and  waste  water  are  conducted  from  the  mill  in  a  flume 
to  the  plant,  and  there  divided  into  two  equal  streams  by  the  insertion 
of  an  adjustable  division  plate  in  the  flume.  The  divided  pulp  passes 
into  boxes  (see  Fig.  40)  4'  long  and  1'  wide,  and  having  steel  screen  bot- 
toms with  i"  and  ^V'  perforations,  set  on  a  reversed  grade  of  6"  to  the 
box.    The  object  of  these  screens  is  to  prevent  any  chips,  leaves,  lint,  or 


56 


CALIFORNIA   GOLD    MILL    PRACTICES. 


foreign  substance  from  passing  into  the  sizing-box  (Fig.  41)  beneath, 
which  consists  of  a  wooden  V-shaped  trough,  6'  long,  15"  broad  at  the 
top  and  2"  in  the  bottom,  constructed  of  IV'  boards.  A  piece  of  canvas 
is  tacked  on  the  bottom  for  packing;  underneath  is  nailed  a  piece  of 
scantling,  4"x6",  at  one  end  of  which,  reaching  within  2"  of  the  end  of 
the  box  proper,  a  slot,  14"  long  and  2"  broad,  is  cut;  here  a  flattened, 
galvanized-iron  funnel,  ending  in  a  2"  pipe,  is  attached.  The  pulp  falls 
through  the  screen  with  some  force  and  is  considerably  agitated  in  the 


Fig.  40. 

separator-box.  Naturally  the  coarser  and  heavier  particles  have  a  ten- 
dency to  settle  toward  the  bottom.  Were  the  outlet  there  large  enough, 
all  the  pulp  would  pass  down  and  out.  Its  size  of  2"  causes  the  box  to 
fill  to  the  height  of  a  sluice-box  in  the  end,  through  which  the  finer  pulp 
fiows  to  the  canvas-tables.  To  facilitate  the  separation,  a  device  is  placed 
in  the  lower  end,  consisting  of  an  iron  pipe,  ^"inside  diameter,  connected 
with  the  main  pipe  above  the  screen,  and  divided  into  two  sections, 
which  are  connected  by  rubber  hose  for  ready  detachment.  The  lower 
6"  of  the  iron  pipe  has  small  perforations,  through  which  clear  water  is 
ejected,  causing  an  agitation  of  the  pulp.  The  end  of  the  pipe  is  stopped 
with  a  wooden  plug,  easily  removed.  The  agitation  at  the  end  of  the 
pipe  causes  the  fine  material  to  be  carried  upward  and  into  the  sluice 


j/DS  y/^'/p'. 


P€/?SPEC  T/l/£ 


E/VD 


Fig.  4L    Sizixg-Box. 


,  Jfi/gB£/rHOS£ 


at  the  end  of  the  separator-box.  Only  coarse  sand  passes  through  the 
bottom  pipe,  and  on  examining  this  with  a  magnifying  glass,  very  few 
particles  of  sulphurets  are  discernible.  This  separator  works  well,  and 
disposes  of  a  lot  of  coarse,  valueless  material  that  would  otherwise  inter- 
fere with  the  subsequent  working  of  the  slimes  on  the  canvas  platforms. 
The  fine  pulp  flowing  from  the  top  of  the  separator  is  conducted  in  a 
sluice  to  a  broad,  flat  box,  in  which  the  stream  is  divided  by  partitions 
into  ten  separate  currents,  each  terminating  over  a  canvas-table,  ten  in  a 


CALIFORNIA   GOLD    MILL    PRACTICES.  57 

row.  The  pulp  goes  over  a  spreader  made  of  strips  of  galvanized  iron, 
I"  in  height,  radiating  from  a  common  center  to  the  farthest  side  of 
the  table,  which  is  12'  wide.  These  strips  are  nailed  to  an  inclined 
board  extending  across  the  canvas-table,  having  an  iron  strip,  1"  high, 
fastened  to  the  lower  end,  perforated  or  notched,  with  indentations  yV' 
deep  and  1"  long,  affording  a  perfect  distribution.  Twenty  tables  are 
arranged  in  two  rows  of  ten  each,  covered  with  canvas  laid  crosswise 
and  overlapping  about  2".  These  tables  have  a  grade  of  1^"  to  the  foot, 
are  13'  long  and  12'  wide.  After  receiving  the  flow  for  an  hour,  it  is 
shut  oS'  from  the  table  and  a  flow  of  clear  water  turned  on,  which  in  a 
few  minutes  washes  away  the  sand,  when  it  is  also  stopped;  then  with 
a  hose  ending  in  a  flat  nozzle,  the  accumulated  sulphurets  are  washed 
from  the  canvas  into  a  trough  below,  extending  along  the  base  of  the 
entire  series.  In  order  to  secure  sufficient  fall  for  this  sluice,  each  suc- 
ceeding table  is  set  4"  lower  than  its  predecessor,  giving  40"  fall  on  125' 
of  sluice  length.  Two  extra  tables  are  arranged,  one  at  the  end  of  each 
row,  to  take  up  the  surplus  flow  during  the  time  one  of  the  tables  is 
shut  of}',  to  avoid  overloading,  as  each  table  already  carries  the  proper 
amount  of  pulp.  The  effectiveness  of  the  canvas-tables  depends  on 
maintaining  an  even  flow  of  pulp  during  a  given  time;  it  will  not  do 
to  overload  them.  All  the  pulp  that  leaves  the  table  is  considered 
waste,  and  is  collected  in  a  flume,  to  be  used  a  short  distance  ofi"  as 
power  on  an  overshot  wheel,  by  means  of  which  the  patentee  runs  a 
vanner  of  his  own  invention.  This  waste  water  is  caught  up  again  and 
used  on  a  second  wheel,  which  also  runs  a  vanner.  The  sulphurets 
washed  from  the  tables  flow  through  a  sluice  to  a  box  outside  the 
building,  12'  long,  2'  wide,  and  12"  deep,  with  a  cross-piece  2'  from  its 
upper  end,  reaching  within  2"  of  the  top  of  the  box;  in  this  upper  sec- 
tion the  coarser  grade  of  the  material  is  retained,  while  the  finer  flows 
over  the  weir.  The  two  grades  are  shoveled  out  separately  and  placed 
in  separate  V-shaped  boxes,  over  which  are  perforated  iron  pipes,  from 
which  small  streams  of  water  trickle,  gradually  carrying  the  pulp  down 
and  passing  it  through  sluices  onto  the  spreaders  of  separate  vanners. 
These  two  machines  work  with  diflerent  motions,  doing  excellent  work 
on  this  impalpably  fine  stuff.  The  slimes  flowing  from  the  washing- 
boxes  beneath  these  vanners  are  conducted,  with  the  overflow  of  the 
two  compartment  boxes  above  referred  to,  to  two  other  canvas-tables, 
below  which  they  are  allowed  to  escape  as  waste;  not  that  they  have 
given  up  all  the  precious  metal  they  carried,  but  because  the  point  is 
reached  where  it  is  more  economical  to  lose  the  remnant  than  to  attempt 
to  save  it. 

As  the  slimes  from  most  of  the  canvas  plants,  as  usually  operated 
(especially  where  the  ore  crushed  carries  a  heavy  percentage  of  sulphu- 
rets, or  has  been  stamped  with  a  high  discharge),  are  still  valuable  in 
gold,  they  can  be  conveyed  to  so-called  slime-settlers,  or  tanks.  These 
tanks,  for  there  are  generally  several,  are  placed  below  the  canvas  plat- 
forms, and  are  about  2'  deep,  2'  wide,  and  12'  to  20'  long;  they  are 
divided  into  sections  of  2'  square,  by  2"  plank  set  on  edge,  extending 
alternately  from  each  side,  leaving  an  opening  4"  wide  and  2'  deep, 
causing  the  slime  water  to  take  a  serpentine  course  in  pas.sing  through. 
The  tanks  stand  level,  and  the  slimes,  in  settling,  form  their  own  grade 
as  they  enter  at  one  end  of  the  tank,  and,  passing  through  the  succes- 


I 


58  CALIFORNIA    GOLD    MILL    PRACTICES. 

sive  sections,  issue  at  a  diagonally  opposite  point  only  slightly  clouded. 
These  tanks  require  cleaning  only  at  long  intervals. 

Up  to  the  present  time,  the  concentrates  in  the  California  mills  have 
been  generally  handled  by  the  chlorination  process,  to  free  them  from 
their  gold,  but  within  the  last  year  several  plants  are  successfully  work- 
ing them  by  the  cyanide  process. 

The  tendency  in  the  construction  of  mills  at  the  present  day  is  to  a 
substitution  of  steel  for  iron,  where  possible,  and  to  an  increase  in  the 
weight  of  the  stamps. 

A  greater  application  of  grinding  and  amalgamating  machines,  in 
place  of  or  subsidiary  to  the  stamp-mill,  rs  also  noticeable,  the  most 
popular  of  which  will  be  shortly  described. 

For  a  more  thorough  appreciation  and  knowledge  of  the  work  done  by 
mills,  records  should  be  kept,  by  the  amalgamator,  of  all  transactions 
connected  with  mill  work,  showing  every  item,  loss  of  time,  consump- 
tion of  mercury,  iron,  fuel,  water,  amount  of  rock  treated,  etc.,  in  addi- 
tion to  the  records  kept  in  the  assay  office.  This  is  already  being  done 
to  some  extent,  but  such  records  should  be  kept  in  the  small  mills  as 
thoroughly  as  in  the  large  ones. 

GRINDING    AND    AMALGAMATING    MACHINES. 

Arrastras. — Although  the  arrastra  has  been  largely  superseded  by  the 
stamp-mill,  the  fact  remains  that  it  is  the  best  and  cheapest  all-round 
gold-saving  appliance  we  have.  Hence,  its  use  is  always  indicated 
where  small,  rich  veins  are  worked  in  the  higher  mountain  regions,  but 
it  is  also  found  valuable  placed  below  the  present  quartz  mill,  where 
the  waste  waters  from  the  mill  can  be  picked  up  and  used  over  again 
for  power  on  horizontal  or  overshot  wheels.  In  these  cases,  it  handles 
the  tailings  from  the  mill  after  they  have  passed  over  the  concentrators 
and  canvas-plants.  This  part  of  the  milling  is  usually  leased  to  parties 
who  pay  the  mine  a  fixed  amount  per  ton  for  the  tailings,  the  lessees 
putting  up  all  their  own  machinery.  These  arrastras  are  built  of  a  size 
to  handle  at  least  4  tons  of  tailings  in  twenty-four  hours.  Their 
foundations  are  either  formed  of  hard  rammed  clay,  concrete, '  or  a 
plank  platform  with  broken  joints,  on  which  a  bed  of  clay  is  placed. 
The  foundation  is  always  made  larger  than  the  circumference  of  the 
proposed  arrastra.  The  bed  is  formed  of  rocks  harder  than  the  sub- 
stance to  be  crushed,  usually  fine-grained  basalt,  granite,  or  quartzite. 
These  are  picked  with  a  partially  level  surface,  and  as  near  of  the  same 
thickness  as  possible,  usually  from  1'  to  2'  thick.  They  are  built  around 
a  center  cone,  forming  an  annular  ring  from  2^'  to  6'  wide,  and  are  laid 
with  narrow  spaces  between  each  rock,  into  Avhich  dry  clay  should  be 
tightly  rammed  to  within  an  inch  of  the  surface.  The  outer  circle  is 
formed  of  rocks  or  staves,  with  rammed  earth  behind,  and  built  from 
2'  to  4'  in  height.  On  the  central  cone,  which  consists  of  stone  or  a 
block  of  wood,  and  which  stands  somewhat  above  the  paved  bottom,  a 
center  post  is  let  in,  from  which  project  four  arms  at  right  angles  to 
each  other,  and  extending  nearly  to  the  outer  circle.  Heavy,  hard  rock- 
drags,  weighing  from  200  to  1,000  lbs.  each  (from  400  to  600  lbs.  is  the 
usual  weight),  are  attached  to  the  arms  by  ropes  or  chains  passing 
through  eye-bolts  secured  in  the  rock- drags.  They  are  placed  so  that 
part  of   them  drag  near  the  cone,  with   the  inside  corner  slightly  in 


CALTFOKMA    GOT.D    >riLL    PRACTICES. 


59 


WW.^' 


TEAM-PowtK  Ai.!;.-i^t::  \,    l\Ei.:    i 'oin  rv. 


60  CALIFORNIA    GOLD    MILL    PRACTICES.  j 

advance,  while  the  remainder  sweep  near  the  outer  circle  with  the  outer 
corner  in  advance.  The  front  edge  should  always  be  slightly  elevated, 
so  as  to  permit  of  the  particles  passing  under  the  drag  instead  of  being 
pushed  ahead. 

Where  a  horizontal  wheel  is  used,  the  arms  are  attached  to  the  center 
post  and  the  wheel  encircles  the  arrastra,  the  water  striking  on  buckets 
set  to  an  angle  of  45°.  With  overshot  wheels  the  arrastra  may  be  run 
by  a  belt  and  pulley  attached  to  the  center-post,  or  by  a  spur  gearing. 
It  requires  about  6  H.  P.  to  run  an  average-sized  arrastra.  Running 
tailings,  a  speed  of  15  to  30  revolutions  per  minute  is  given;  crushing 
ore,  the  arrastra  should  be  run  slower  and  the  pulp  thicker. 

For  discharging  the  arrastra,  plug-holes  at  different  levels  are  put 
into  the  outer  circle,  leading  the  pulp  into  sluices  lined  with  plates, 
riffles,  and  blankets.  In  some  cases  the  arrastra  has  been  made  to  work 
continuously  by  fitting  a  screen  to  a  part  of  the  outer  circle  and  letting 
it  discharge  into  a  line  of  sluices.  As  the  arrastra  bottom  and  drags 
are  extremely  uneven  and  rough  when  first  set  up,  some  coarse  sand 
and  water  are  introduced  on  first  starting,  and  the  drags  are  allowed  to 
run  slowly  until  somewhat  smoothed  down,  before  the  regular  charge  is 
introduced.  The  machine  is  usually  only  cleaned  up  thoroughly  when 
the  bottom  is  worn  away;  between  times  the  crevices  are  picked  out  for 
the  depth  of  an  inch  or  two  with  picks,  scrapers,  and  spoons,  and 
panned  out,  with  what  pulp  remains  on  the  bottom,  after  the  charges 
have  been  successively  thinned  down  and  run  off  through  the  plug- 
holes. If  crevicing  has  been  done,  a  little  fresh  clay  can  be  rammed  in 
to  within  1"  of  the  top  of  the  bed.  During  the  grinding  of  the  charge, 
the  quicksilver  is  introduced  through  a  cloth;  the  amalgam  should  be 
kept  drier  than  in  the  stamp  battery,  though  not  sufficiently  so  as  to 
become  "  crumbly."  Great  attention  must  be  paid  to  tamping  the  bed 
in  solid,  otherwise  an  excessive  loss  of  quicksilver  may  occur.  Continual 
horn  tests  of  the  pulp  furnish  a  guide  for  the  proper  working. 

Machines  have,  from  time  to  time,  been  introduced  in  California  to 
replace  stamps,  claiming  to  do  more  effective  work,  both  as  regards  the 
crushing  as  well  as  the  amalgamating.  Those  mostly  seen  in  opera- 
tion, and  finding  the  most  favor,  are  the  Huntington  and  the  Bryan 
mills,  which  may  be  taken  as  types,  and  which  reduce  the  ore  by  a  con- 
tinuous rolling  motion;  in  the  one  case  the  roller  acting  on  a  ring  on 
the  circumference,  and  in  the  other  on  dies  in  the  bottom. 

The  Huntington  Mill  consists  of  a  shallow  iron  pan  with  a  central 
cone,  through  which  an  iron  shaft  revolves.  Bolted  on  the  sides  of  the 
pan  and  inclosing  it,  are  semi-circular  iron  sections  made  in  two  halves 
and  also  bolted  together;  one  of  these  sections  contains  an  opening 
about  9"  deep,  divided  into  three  parts,  into  which  curved  iron  screen- 
frames  are  keyed,  while  the  other  section  contains  a  feed-trough, 
attached  near  the  top.  Between  the  bottom  of  the  pan  and  the  lower 
edge  of  the  screen-frames  an  iron  or  steel  ring-die  fits  against  the  sides  of 
the  shallow  pan,  being  secured  by  wooden  wedges;  against  this  die,  four 
rollers,  suspended  from  yokes  resting  on  an  iron  cover,  revolve,  receiving 
their  motion  from  the  central  shaft.  These  suspended  rollers  are  pressed 
by  centrifugal  force  against  the  ring-die.  Each  roller  is  encircled  by 
an  iron  or  steel  shoe  fastened  by  wooden  wedges;  this  can  be  renewed 
when  worn  too  thin,  or  when  it  becomes  unround — flattened.     Means 


CALIFORNIA    GOLD    MILL    PRACTICES. 


61 


are  provided  for  lubricating  the  shafts  on  which  the  rollers  work,  with- 
out permitting  the  lubricant  to  come  in  contact  with  the  pulp.  As  the 
rollers  hang  about  V'  above  the  bottom  of  the  pan,  scrapers  are  attached 
to  the  revolving  cover  between  the  rollers,  and  reaching  to  the  bottom 
of  the  pan,  to  prevent  the  baking  of  the  pulp. 

The  size  of  the  pan  most  frequently  used  is  5'  in  diameter,  though  for 
prospecting  purposes  one  of  3^'  is  also  made ;  the  former  is  run  at  a 
speed  of  70  revolutions  per  minute,  the  latter  at  90  revolutions.  They 
are  provided  with  self-feeders,  which  introduce  the  ore  at  regular  inter- 
vals— the  only  wa}-  in  which  they  can  be  operated,  though  not  correct  in 


Fig.  42.    Thb  Huntington  Mill. 

principle.  A  5'  mill  requires  about  8  H.  P.,  and  crushes  about  20  tons 
per  day.  Before  starting  up  a  certain  amount  of  quicksilver,  up  to  50 
lbs.,  is  introduced  into  the  pan  with  some  water  and  rock.  Tiie  supply 
should  be  regulated  to  make  a  stiffer  pulp  than  in  a  stamp-battery  ; 
quicksilver  is  added  from  time  to  time.  A  groove  in  the  bottom  of  the 
pan,  connecting  with  a  plug-hole  on  the  outside,  permits  of  the  quick- 
silver and  amalgam  being  drawn  olF  at  intervals  to  recover  the  latter, 
after  which  the  former  is  returned.  If  the  pan  is  working  correctly  the 
bottom  around  the  center  remains  bare  ;  this  can  be  observed  through 
the  cover  while  running  ;  when  not  bare,  it  is  a  sign  that  the  pan  is 
being  overfed.  As  the  machine  throws  the  pulp  with  considerable 
violence  through  the  curved  screens,  a  shield  is  placed  outside  of  them, 
directing  the  pulp  into  a  narrow  sluiceway  with  a  spout  opening  on  the 
apron-plate.  It  is  claimed  that  the  percentage  of  gold  amalgamated 
and  saved  on  the  inside  is  f-AV  greater  than  in  the  stamp-mortar,  going 
above  80%;   all  rusty  gold  being  subjected  to  a  heavy  scouring  action. 


I 


62 


CALIFORNIA    GOLD    MILL    PRACTICES. 


The  Russian-iron  screens  used  are  short-lived  ;  they  can  be  made  to 
last  somewhat  longer  by  placing  a  false  screen,  made  from  an  old  worn 
screen  with  the  openings  enlarged,  between  the  pulp  and  the  screen 
proper. 

Great  care  must  be  exercised  in  putting  up  one  of  these  machines,  to 
get  it  perfectly  level  and  on  a  rigid  foundation,  and  to  keep  all  the  bolts 
holding  the  pan  on  the  foundation  well  tightened  up  ;  the  ieed  also 
requires  close  observation. 

When  cleaning  up  or  renewing  the  ring-dies  or  shoes,  the  top  cover, 
with  the  suspended  rollers,  are  lifted  out  with  chain  block  and  tackle, 
leaving  the  interior  of  the  pan  free  for  operation. 

The  mill  works  well  on  soft  quartz  and  clayey  ores,  introduced  in 
pieces  not  larger  than  walnuts.  A  great  drawback  to  the  machine  is 
that  the  rings  on  the  rollers  and  also  the  dies  become  "unround, ''  so  that 
instead  of  rolling  smoothly,  they  strike  in  places,  necessitating  changing 
the  rings  before  they  are  worn  out;  this  changing  takes  up  some  time. 


Thk  Bryan  Mill. 


The  opinions  of  millmen  who  have  handled  the  Huntington  mill,  as  to 
its  merits,  are  very  diverse.  Where  the  ore  produces  a  large  amount  of 
fine  stuflf,  by  using  a  grizzly  with  closely  set  bars,  the  Huntington  can  be 
run  to  advantage  on  these  "smalls"  in  conjunction  with  the  stamps. 

The  Bryan  Roller  Mill  is  a  modified  form  of  the  Chili  mill,  built  in 
sizes  of  4'  and  5'  diameter.  It  consists  of  an  annular  mortar  with  an 
outside  gutter  and  spout,  cast  solid,  containing  steel  dies  arranged  in  the 
track  of  three  crushing  rollers,  which  in  the  5'  mill  have  a  crushing- 
face  of  7",  a  diameter  of  44",  and  weigh  3,650  lbs.  They  have  fixed 
axles,  "journaled"  in  a  central  revolving  table,  attached  to  and  driven 
by  a  belt  pulley.  This  pulley  is  a  cylindrical  tank,  which,  in  the  smaller 
pattern,  rests  immediately  on  the  rollers,  and  can  be  made  to  increase 
their  crushing  power  by  being  loaded.  The  mortar  is  supplied  with 
curved  screen-frames  around  the  entire  machine,  the  pulp  being  dis- 
charged all  around  into  a  gutter  delivering  through  a  spout,  on  one  side, 
to  an  apron-plate. 


CALIFORNIA   GOLD    MILL    PRACTICES. 


63 


The  chief  wearing  parts  are  the  steel  dies  and  tires  on  the  rollers; 
these  latter  are  fastened  to  the  rollers  by  wooden  wedges.  According  to 
the  statement  of  the  manufacturers  (Risdon  Iron  Works,  San  Fran- 
cisco), one  set  of  these  wearing  parts  will  crush  from  4,000  to  8,000  tons 
of  ore  in  the  large  size,  and  1,500  to  2,000  tons  in  the  smaller  size,  and 
at  the  rate  of  25  to  35  tons  and  12  to  20  tons  per  day,  with  a  speed  of 
30  and  60  revolutions,  respectively,  per  minute,  the  smaller  size  requir- 
ing from  5  to  6  H.  P.  The  oil  channels  for  lubricating  the  bearings  are 
arranged  to  prevent  the  oil  from  entering  the  mortar.    To  keep  the  pulp 


Fig.  44.    The  Oriffix  Mill. 


from  baking  to  the  rollers  or  dies,  and  to  assist  in  equalizing  the  ore 
received  from  the  feeder,  scrapers  with  adjustable  springs  follow  each 
roller.  They  are  also  provided  with  self-feeders.  In  operating  the  mill, 
ore,  water,  and  mercury  are  introduced  into  the  mortar,  the  pulp  passing 
around  next  the  screens  in  a  current  not  less  than  300' per  minute,  while 
the  motion  inside  of  the  rollers  is  much  slower.  The  amalgam,  working 
its  way  toward  the  center  cone,  is  kept  from  being  re-ground,  and  can  be 
observed  while  the  mill  is  in  operation;  it  is  claimed  to  retain  80%  of  the 
amalgam  in  the  mortar.  To  clean  it  up,  the  dies  between  the  rollers  are 
removed,  the  pulp  and  amalgam  taken  out,  and  wooden  blocks  of  the 
thickness  of  the  die  put  in  their  stead,  on  which  the  rollers  are  revolved, 
when  the  remaining  ones  can  betaken  up.     It  is  claimed  for  these  mills, 


64  CALIFORNIA    GOLD    MILL    PRACTICES. 

that  they  wear  smooth,  and  even  while  crushing  hard  quartz,  dis- 
charge freely  (on  account  of  large  screen  area),  avoid  sliming  and  flour- 
ing of  quicksilver,  ai*e  good  amalgamators,  can  be  cleaned  rapidly,  are 
easily  put  in  place,  and  require  small  power  for  amount  of  work  done. 

The  Griffin  Mill  belongs  to  that  class  of  mills  using  a  roll  running 
against  a  ring  or  die;  but  instead  of  several  rollers,  as  in  the  Huntington, 
this  has  one  roller  only,  swinging  from  a  longer  shaft,  hung  from  a  point 
in  the  central  axis  of  the  mill,  and  rotated  about  its  own  axis  by  the 
power  applied  at  the  top.  It  is  run  at  a  speed  of  190  to  200  revolutions 
per  minute,  crushing  from  1^  to  2\  tons  per  hour,  the  power  being 
applied  to  a  horizontal  pulley  above,  from  which  the  shaft  is  suspended 
with  a  universal  joint,  and  the  roller  is  rigidly  attached  to  the  lower 
extremity  of  the  shaft.  The  roller  swings  in  a  circular  pan  supplied 
with  a  ring  or  die,  against  which  the  roller  works;  and  carries  on  the 
under  side  scrapers  or  plows  to  prevent  the  pulp  from  baking.  A  circular 
screen-frame  is  fastened  on  the  pan,  to  the  top  of  which  a  conical  shield 
is  attached  at  the  apex,  through  which  the  shaft  works.  The  pulley 
revolves  upon  a  tapered  and  adjustable  bearing,  supported  by  the  frame 
composed  of  iron  standards,  two  of  which  are  extended  above  the  pulley 
to  carry  the  arms  in  which  is  secured  the  hollow  journal-pin.  The  shaft 
is  suspended  to  a  universal  joint  within  the  pulley.  This  joint  is  com- 
posed of  the  ball  or  sphere  with  trunnions  attached  thereto,  which  work 
in  half  boxes  that  slide  up  and  down  recesses  in  the  pulley-head  casting. 
The  lubricant  is  supplied,  for  all  parts  needing  it,  through  the  hollow 
pin.  The  roll  revolves  within  the  ring-die  in  the  same  direction  that 
the  shaft  is  driven,  but  on  coming  in  contact  with  the  die,  it  travels 
around  the  die  in  the  opposite  direction  from  that  in  which  the  roll  is 
revolving  with  the  shaft.  A  pressure,  by  centrifugal  force,  of  6,000  lbs. 
is  brought  to  bear  on  the  material  being  pulverized  between  the  roll  and 
die.  The  water  is  introduced  with  feed  when  running,  and  receives  a 
whirling  motion  from  the  roll,  which  brings  the  pulp  against  the  screens, 
9'  in  area.  A  circular  trough  on  the  outside  of  the  pan  conducts  the 
pulp  to  one  side,  where  it  discharges  over  an  apron. 

TYPICAL    CALIFORNIA    GOLD    MILLS. 

As  the  details  in  milling  practices  of  the  several  counties  of  the  State 
vary  greatly,  the  following  typical  mills  have  been  selected  to  indicate 
the  practice  under  varying  conditions: 

No.  1.  Amador  County. — The  ore  is  a  soft,  easily  crushed  quartz,  with 
about  1-5%  sulphurets,  and  is  largely  mixed  with  slaty  material,  which, 
to  the  extent  of  25%,  is  found  mixed  with  the  concentrates.  The 
stamps  weigh  750  lbs.  each,  and  drop  6"  about  ninety-five  times  per 
minute,  discharging  through  a  No.  8  slot  screen,  at  the  rate  of  2\  tons 
per  stamp  in  twenty-four  hours.  The  stamps  drop  in  the  following 
order:  1,  2,  3,  5,  4;  Nos.  1  and  2  having  \"  more  drop  than  the  other 
stamps;  in  the  adjoining  battery  the  order  is  reversed.  Iron  shoes  and 
dies  are  used.  There  is  an  inside  plate  used  in  the  battery,  which 
retains  about  75%  of  the  amalgam.  The  apron  is  48"xl3",  set  on  a 
grade  of  |"  to  the  foot,  and  the  double  sluices  below  are  9'  long  by  14" 
wide,  with  a  grade  of  \\"  to  the  foot.     From  these  sluices  the  pulp 


CALIFORNIA    GOLD    MILL    PRACTICES. 


65 


passes  to  vanners.  To  clean  the  sulphurets  from  the  slaty  admixture, 
a  cradle,  12'  long,  20"  wide,  and  4"  deep,  has  been  placed  in  the  mill' 
run  by  an  eccentric.  The  dirty  slimy  sulphurets  are  taken  from  the 
washing-boxes  beneath  the  vanne  and  placed  in  a  half  barrel  standing 
on  the  floor  of  the  mill,  into  which  a  hose  is  lowered,  and  the  sulphurets 

INJECTOR  DEVICE 
fo/f /PA/S//VC  &  CLEANING  PULP 


Fig.  45. 

are  raised  from  the  barrel  to  tlie  cradle  by  creating  a  vacuum,  through  a 
small  jet  of  water  under  pressure  forming  an  ejector.  The  pulp  in  the 
cradle  is  stirred  vigorously  toward  the  head;  the  grade  is  from  7"  to  8" 
in  12'.  This  washing  in  the  cradle  relieves  the  pulp  of  about  25%  of 
Avaste  material.  Twelve  tons  can  be  washed  in  a  day.  The  canvas- 
plant  below  the  vanner  has  some  interesting  features.  The  canvas 
strips  are  only  12"  wide.  The  pulp  as  it  leaves  the  vanner  is  carried 
to  a  mercury-trap,  consisting  of  a  box  of  diminishing  width,  with  three 

QU/C/^S/Ll/f:/?  TffAP. 

ricr^s    |__r>9/?/P 


/iOff/ZO/VTAL  5£CT/0A/ 


0/ST/7/3ar£ff 

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Fig.  46. 


upright  divisions,  under  and  over  which  the  pulp  flows.  P>om  the 
mercury-trap  the  pulp  falls  into  a  long  box,  about  1'  square  at  the  ends, 
in  the  bottom  of  which  are  ten  holes,  whose  size  is  regulated  by  experir 
ence;  they  must  equalize  the  discharge  with  the  inflow  from  the  mer- 
cury-trap.    The  pulp  introduced   into  the   long   distributor-box    sizes 

5 — GMP 


66 


CALIFORNIA   GOLD    MILL    PRACTICES. 


itself  to  some  extent  by  gravity;  the  finer  material,  being  held  in  sus- 
pension longer,  finds  its  way  out  at  the  end  of  the  box,  while  the  coarse 
quickly  passes  through  the  holes  in  the  bottom,  nearer  the  center  of  the 
box. 

There  are  twelve  strips  of  canvas,  100'  in  length,  each  strip  having  a 
width  of  12"  and  a  grade  of  4^"  in  12'.     The  coarse  material  is  all  found 

C/^Nl//JS  T/=rBL£: 


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Fig.  47. 

on  the  six  center  sections,  the  two  outside  sections  on  each  side  carry- 
ing the  finer  material.  An  additional  series  of  tables,  with  20"  wide 
sections  and  a  grade  of  9"  in  12',  receives  the  pulp  after  passing  over  the 
first. 


No.  2.  Amador  County. — The  practice  of  this  mill  in  handling  their 
tailings  may  be  taken  as  an  example  of  the  better  methods  now  prac- 
ticed in  the  State.  This  mill  has  900-lb.  stamps,  dropping  85  times  per 
minute,  with  a  6"  drop  and  a  7"  discharge,  kept  constant  by  the  use 
of  lower  chock-blocks.  No.  30  brass- wire  screens,  4'  long  and  4"  wide, 
set  vertical,  are  used,  giving  a  duty  per  stamp  of  2^  tons  in  twenty-four 
hours.  The  batteries  are  supplied  with  inside  front  plates.  The  apron- 
plates  are  46"x30",  set  on  a  grade  of  If"  to  the  foot.  These  are  followed 
by  18'  of  sluice-plates,  15"  wide,  the  first  10'  of  which  are  double. 
About  66%  of  the  amalgam  is  recovered  in  the  battery.  The  loss  in 
quicksilver,  which  is  introduced  into  the  battery  every  half  hour, 
amounts  to  about  1^  cents  per  ton.     The  total  cost  of  milling  at  these 


CALIFORNIA   GOLD    MILL    PRACTICES.  67 

works  is  given  as  70  cents  per  ton.  The  mill  is  supplied  with  three 
vanners  to  each  battery,  with  4^'  belts.  The  pulp  from  the  plate-sluices 
passes  directly  to  the  spreaders  of  the  vanners,  a  division  into  thirds 
being  first  efiected.  After  leaving  the  belts,  the  pulp  flows  through 
sluices  to  a  flume,  where  it  is  divided  into  two  equal  streams  by  the 
insertion  of  an  adjustable  division  plate  in  the  flume.  The  divided 
pulp  passes  to  two  steel  screens  with  perforations  of  ^"  and  yV'  respect- 
ively, w'hich  form  the  bottoms  of  two  4'  boxes,  1'  wide,  set  on  a  reverse 
grade  of  6"  in  4'.  These  boxes  prevent  any  foreign  substance  from 
passing  through  into  the  sizing-box  below,  and  clogging  the  outflow 
pipes.  After  the  passage  of  the  screens  the  pulp  falls  into  a  separator, 
consisting  of  a  wooden  V-shaped  trough,  6'  long,  15"  wide  on  top  and 
2"  at  the  bottom,  with  a  flat,  funnel-shaped  discharge  pipe  of  galvanized 
iron  attached  at  one  end,  ending  in  a  round  2"  pipe.  As  more  pulp 
enters  the  separator  than  can  be  discharged  through  the  2"  pipe,  it  fills 
and  flows  over  the  end  into  a  launder;  the  heavier  and  larger  particles 
sinking  down  and  passing  through  the  pipe.  The  overflow  passes  on  a 
spreader  that  delivers  it  to  a  canvas-table,  with  ten  sections;  a  second 
similar  table,  placed  below,  receives  the  waste  from  the  first  one.  The' 
tables  are  12'  wide,  13'  long,  and  set  on  a  grade  of  1^"  to  the  foot,  and 
to  secure  a  proper  grade  for  the  waste-sluice,  each  section  is  set  4"  below 
its  predecessor.  All  the  waste  water  passing  from  the  tables  is  used  a 
short  distance  off  as  power  on  an  overshot  wheel  that  runs  a  vanner, 
on  which  are  worked  the  concentrates  taken  from  the  tables. 

No  3.  Butte  County. — The  quartz  carries  considerable  sulphurets. 
When  hoisted  from  the  mine  it  is  dropped  immediatel}'^  over  a  grizzly, 
with  the  bars  placed  H"  apart;  the  coarse  rock  crushed  is  loaded  into 
cars,  and  trammed  to  the  mill,  distant  about  150  yards,  and  dumped 
into  bins  which  are  calculated  to  carry  1,500  tons.  From  here  chutes 
convey  the  ore  to  the  Challenge  self-feeders.  These  are  operated  from 
the  center  stamp  in  each  battery.  The  stamps,  which  are  supplied  with 
steel  shoes  and  dies,  weigh  850  lbs.,  drop  7",  and  about  100  times  per 
minute;  the  discharge  is  7";  the  screen  is  No.  8  diagonal-slot,  8"  wide; 
each  stamp  crushes  2-J  tons  per  twenty-four  hours.  The  screens,  which 
last  about  four  weeks,  are  used  later  in  the  chlorination  works  for  the 
recovery  of  cement  copper.  From  the  mortar  the  pulp  passes  over  a 
14"  mortar  plate;  thence  to  a  4'  apron  and  12'  of  sluice-plates;  aprons 
and  plates  are  set  to  a  grade  of  3"  to  the  foot.  The  pulp  then  passes 
over  the  vanners,  two  for  each  battery,  after  leaving  which,  it  is  con- 
veyed to  the  canvas-platform  house.  The  canvas-platform  is  24'  wide 
and  60'  long,  covered  with  x  2  0  0  canvas,  and  below  it  are  150'  of 
settling-boxes.  The  plates  are  scraped  every  day,  and  dressed  besides, 
when  required. 

No.  4.  Calaveras  County. — The  rock  consists  of  massive  quartz, 
schistose  and  slaty  diabase,  and  chloritic  and  talcose  schist,  with  iron 
sulphurets;  it  is  crushed  in  jaw-breakers  at  the  head  of  the  shaft,  after 
passing  over  grizzlies,  and  is  dropped  into  bins,  from  which  the  ore  is 
conveyed,  in  cars,  to  three  other  bins  in  the  mill,  one  for  each  section  of 
twenty  stamps,  having  a  capacity  of  600  tons  each.  The  bins  discharge 
into  Challenge  self-feeders.  The  sixty  stamps  weigh  775  lbs.  each,  and 
drop  105  times  per  minute,  the  drop  being  6",  and  the  discharge  10" 


I 


68  CALIFORNIA   GOLD    MILL    PRACTICES. 

from  the  new  die.  Only  one  chock-block  is  used,  causing  the  height  of 
discharge  to  constantly  increase.  The  duty  of  the  stamps  is  4  tons  in 
twenty-four  hours.  Round-punched  tin  screens,  10"xl4",  are  used. 
They  are  lightly  burned  before  using.  Three  and  a  half  of  the  screen 
sheets  are  tacked  on  the  screen-frame  on  three  sides;  the  top  side  is 
secured  by  a  long,  narrow  strip  of  wood  screwed  to  the  frame.  The 
superficial  area  of  the  discharge  is  about  287  sq.  in.  The  screen-frame 
is  braced  by  six  cross-ribs,  to  which  the  screens  are  tacked.  A  splash- 
board is  suspended  in  front  of  the  screen  by  eyebolts  and  hooks,  with  a 
strip  of  canvas  tacked  along  the  bottom,  the  full  width  of  the  screen. 
An  iron  apron  or  table  is  secured  to  the  front  of  the  mortar  below  the 
screen,  the  bottom  of  which  falls  1"  below  the  lip  of  the  mortar,  permit- 
ting the  insertion  of  a  rough  inch  board,  9"  in  width,  in  front  of  the 
mortar,  flush  with  the  upper  edge  of  the  lip  of  the  mortar;  on  this  the 

Plates  /r^ rfiONT  or  MoRrflR 

3. 3o/f/?o. 
^  Tftoi/Gfy. 
J.  Plate. 
6.  HFffOA/ 


Fig.  48. 

pulp  falls  from  the  screen,  and  it  is  claimed  to  be  superior  to  a  plate  in 
retaining  the  amalgam.  Three  inches  below  the  board,  runs  a  trough, 
in  which  are  two  apertures  one  third  the  distance  from  each  end,  which 
allows  the  pulp  to  fall  on  a  short,  6"  wide  copper  plate  with  a  pitch 
toward  the  mortar,  and  from  thence  to  the  apron-plate,  2'  wide  and  24' 
long,  set  to  a  grade  of  2"  to  the  foot.  An  inside  front  plate  is  used  in 
the  mortar.  From  the  apron-plate  the  pulp  passes  to  a  sluice-box  and 
is  conducted  to  the  spreaders  of  the  vanners,  of  which  there  are  twenty- 
four.  After  leaving  these,  the  pulp  is  led  through  a  sluice-box  and 
flume  one  mile  long  to  the  canvas-plant.  The  plates  are  dressed  every 
morning;  a  battery  is  hung  up,  the  water  shut  oft",  the  splash-board 
removed  and  washed  oft",  as  also  the  screen  and  the  entire  front  of  the 
battery,  to  remove  all  sand;  the  plate  is  then  vigorously  scoured  with  a 
whisk-broom  to  loosen  the  amalgam.  A  very  dilute  solution  of  cyanide 
of  potassium  is  sometimes  used  during  this  operation,  and  the  loosened 
amalgam  brushed  to  the  foot  of  the  plate.  The  plate  is  then  scraped 
upward  with  a  piece  of  rubber  4"x4"  and  \"  thick;  a  piece  of  rubber 
belting  would  answer  the  same  purpose.  The  collected  amalgam  at  the 
head  of  the  plate  is  removed  in  a  scoop  and  placed  in  a  safe.  The  plate 
is  then  sprinkled  lightly  with  quicksilver,  which  is  spread  evenly  over 
the  entire  plate,  the  water  turned  on,  and  the  stamps  dropped.  The 
operation  for  all  the  plates  requires  nearly  three  hours. 

A  clean-up  of  the  mill  is  made  monthly  or  semi-monthly,  according 
to  the  condition  of  the  battery  amalgam,  at  which  time  all  necessary 
repairs  are  made,  and  new  shoes  and  dies  are  fixed  if  required.  Shortly 
before  hanging  up,  the  feed  is  shut  oft"  to  permit  the  ore  to  be  crushed 
down  as  low  as  possible.  The  water  is  then  shut  off"  from  the  battery, 
splash-board  and  screen  removed,  and  all  hosed  off;  the  inside  plate  is 


CALIFORNIA   GOLD    MILL    PRACTICES. 


69 


removed,  and  the  amalgam  scraped  off  The  contents  of  the  battery- 
are  now  removed,  and  placed  in  the  revolving  clean-up  barrel,  the  dies 
replaced,  tappets  set,  screens  replaced,  and  the  mill  started.  The  pulp 
that  leaves  the  mill  carries  considerable  auriferous  pyritical  slimes,  as 
might  be  inferred  from  the  high  discharge  used  in  the  battery.  This  is 
conveyed  through  a  sluice  12" x8",  to  a  canvas-plant  one  mile  distant. 
Just  before  entering  the  building  set  apart  for  the  recovery  of  these 
slimes,  the  sluice  is  widened  to  18",  and  divided  into  three  sections  by 
two  narrow  strips  fastened  to  the  bottom.  These  divisions  fork  off  into 
separate  sluices,  which  are  again  subdivided.     Three  of  these  subdivis- 


OJSTF/BUrORS. 


Detail  ofGuftei: 


Fig.  49. 


ions  are  carried  directly  through  the  building,  and  there  divided,  and 
the  other  three  are  divided  off  in  five  separate  sluices,  one  for  each  sec- 
tion of  the  canvas-table.  There  are  forty-five  sections  for  each  table — 
ninety  in  all.  They  are  42'  long,  22"  wide,  and  set  on  a  grade  1^"  to 
the  foot.  No.  8  duck  canvas  is  used,  and  when  worn  on  one  side  it  is 
turned;  it  lasts  about  one  year.  The  last  division  of  the  pulp,  outside 
the  building,  is  into  five  boxes,  4"  square,  each  of  which  terminates  in 
a  receiving-box,  reaching  across  three  canvas  sections,  about  bV.  The 
five  divisions  supply  one  third  of  the  sluices  on  one  side  of  the  build- 
ing; the  pulp  passing  to  the  canvas  through  an  auger-hole  in  the  side 
of  the  box.  The  flow  is  regulated  by  a  slide  suspended  over  the  whole. 
Above  the  pulp-distributing  box  is  a  clear-water  box,  and  at  the  lower 
end  of  the  canvas-tables  are  two  sluices,  side  by  side — one  to  receive  the 
concentrates,  the  other  for  the  reception  and  discharge  of  pulp.  The ' 
current  must  be  thinned  and  distributed  so  that  no  accumulations 
form. 


70  CALIFORNIA    GOLD    MILL    PRACTICES. 

No.  5.  El  Dorado  County. — The  quartz  carries  considerable  slate 
mixed  with  it,  and  about  3%  of  iron  sulphurets.  The  stamps  weigh  950 
lbs.  each,  and  drop  4"  104  times  per  minute,  discharging  through  a 
No.  2  sheet-tin,  perforated  screen  with  from  5"  to  7"  discharge,  crush- 
ing 3  tons  per  stamp  in  twenty-four  hours.  The  shoes  and  dies  are  both 
steel.  The  battery  is  supplied  with  an  inside  plate  in  front.  The  apron- 
plates  are  16'  long,  set  on  a  grade  of  1|"  to  the  foot,  and  are  followed 
by  6'  of  sluice-plates,  2'  wide,  on  the  same  grade.  These  plates  are 
dressed  every  day,  but  only  scraped  once  a  month.  (Note: — This  is  not 
advantageous,  as  the  constant  scouring  action  of  the  pulp  undoubtedly 
detaches  fine  particles  of  amalgam.)  The  batteries  yield  62%  of  the 
amalgam.  Eight  Woodbury  concentrators  receive  the  pulp.  The  quick- 
silver is  introduced  into  the  battery  every  half  hour;  the  loss  of  quick- 
silver being  estimated  about  one  pound  to  every  ten  tons  of  ore. 

No.  6.  El  Dorado  County. — The  quartz  carries  about  2%  of  sulphurets 
and  contains  slate  mixed  with  it.  The  stamps  weigh  750  lbs.  each  and 
are  fed  by  Challenge  feeders;  no  rock-breaker  is  used.  The  stamps 
make  96  drops  per  minute,  varying  from  4^"  to  6",  with  7"  discharge. 
The  mortars  are  wide,  and  have  an  8"  wide  inside  amalgamated  plate; 
the  screen  is  perforated  tin,  equal  to  No.  7.  The  apron  is  54"  by  42", 
with  grade  of  1|"  to  the  foot,  followed  by  sluice-plates  12'  long,  which 
are  double  on  one  battery  and  divided  into  four  divisions  on  the  other; 
this  latter  arrangement  gives  better  results.  Below  the  sluice-plates  is 
a  blanket-sluice,  6'  long  and  14"  wide,  the  blanket  being  washed  twice 
a  shift.  From  these  the  pulp  passes  to  the  Frue  vanners  with  6'  belts; 
the  same  wheel  runs  both  stamps  and  vanners.  The  plates  are  dressed 
twice  in  twenty-four  hours,  but  are  not  scraped  until  the  clean-up,  once 
a  month.  One  and  three  quarters  tons  are  crushed  to  the  stamp  per 
twenty-four  hours. 

No.  7.  Mariposa  County. — This  mill  is  working  on  ores  containing 
gold  in  a  very  finely  divided  state.  There  are  ten  stamps  of  900  lbs. 
each,  fed  by  self-feeders.  These  stamps  drop  96  times  per  minute,  with 
a  7"  discharge  while  the  die  is  new;  when  it  is  worn  down  one  half,  a 
smaller  chock-block  is  placed  under  the  screen.  The  pulp  is  retained 
in  the  mortar  for  a  long  time.  The  stamps  are  only  raised  to  the  level 
of  the  water  as  it  stands  in  the  mortar;  and  a  front  inside  plate  is  used. 
The  screen  is  a  60-mesh.  It  is  claimed  that  70%  of  all  the  amalgam 
saved  is  taken  from  the  inside  battery-plate.  There  are  three  apron- 
plates  to  each  battery;  the  first  is  immediately  in  front  of  the  splash- 
board, next  to  the  lip  of  the  mortar,  12"  deep  and  the  width  of  the 
mortar.  This  is  followed  by  a  2"  drop  onto  a  second  plate  3'  deep, 
across  the  width  of  the  mortar,  succeeded  by  a  1"  drop  to  a  4'  apron- 
plate.  From  this  plate  the  pulp  passes  immediately  through  distribut- 
ing pipes  to  the  vanners,  of  which  there  are  three.  Two  of  these  are  4' 
wide,  taking  the  pulp  from  one  battery,  while  a  6'  belt  vanner  takes  the 
pulp  from  the  other  battery.  The  narrow  belt  vanner  gives  the  best 
satisfaction. 

No.  8.  Nevada  County. — The  ore  is  delivered  by  car  at  the  top  of  the 
mill  into  grizzlies,  the  bars  of  which  are  2^"  apart,  and  which  deliver 
the  coarse  stuff  to  a  crusher  of  the  Blake  type,  through  a  bin  with  chute 


CALIFORNIA   GOLD    MILL    PRACTICES,  71 

immediately  over  the  crusher,  keeping  the  same  constantly  supplied 
without  the  aid  of  a  shovel.  From  the  rock-breaker  the  ore  is  delivered 
into  bins  with  chutes  connecting  with  the  Challenge  self-feeders.  The 
feed  is  operated  from  the  center  stamp.  The  stamps  drop  7"  and  86 
times  per  minute,  with  a  4"  discharge.  Steel  shoes  on  iron  dies  are  used. 
The  screens  are  English  sheet-tin,  perforated,  No.  10,  five  pieces  making 
a  complete  screen,  costing  50  cents,  and  lasting  one  month.  The  steel 
shoes  on  iron  dies  have  records  of  over  300  tons  to  the  stamp,  the  daily 
average  being  from  If  to  2  tons  per  stamp.  The  plates  are  divided  into 
an  upper  apron,  18"  wide,  followed  by  a  4'  apron.  Between  the  two, 
catching  the  pulp  from  No.  1,  is  a  box  3"  wide,  with  a  perforated  screen 
bottom,  somewhat  coarser  than  the  battery-screen.  This  acts  as  a 
distributor  on  No.  2  apron,  retaining  any  coarse  pieces.  For  the  forty 
stamps  and  accompanying  concentrators,  15  miner's  inches  of  water  are 
used,  all  applied  on  the  inside  of  the  battery.  The  aprons  have  a  f" 
grade  to  the  foot.  Below  the  apron  are  12'  of  sluice-plates,  part  of  them 
30"  wide,  while  the  others  have  the  same  width  as  the  apron  above. 
These  plates  are  cleaned  up  every  morning  with  pieces  of  rubber  belting; 
it  takes  about  fifteen  minutes  to  clean  one  set.  From  the  sluice-plates 
the  pulp  passes  over  a  12'  shaking-table  covered  with  silver  plates; 
these  plates  receive  their  motion  from  an  eccentric  placed  underneath. 
Passing  the  table  the  pulp  enters  a  box,  from  which  it  is  conveyed 
through  pipes  to  the  vanners  on  a  lower  floor,  two  for  each  battery. 

No.  9.  Nevada  County. — The  stamps  weigh  750  lbs.  each,  drop  6",  95 
times  per  minute,  with  from  4"  to  6"  discharge,  and  crush  from  1|  to  2  tons 
per  day,  using  steel  shoes  and  dies.  There  is  a  5"  wide  silvered  plate  in 
the  front  of  the  battery.  A  No.  9,  perforated,  sheet- tin  screen  is  used; 
it  is  not  burnt  before  putting  on,  and  is  turned  when  the  lower  edge  is 
worn,  lasting  on  an  average  30  days.  In  front  of  the  screen  is  a  splash- 
board, provided  with  an  8"  plate  next  to  the  screen.  The  upper  apron- 
plate  is  18"  deep,  set  on  a  grade  of  |"  to  the  foot,  with  12'  of  apron-plates 
below,  divided  into  four  plates  of  3'  each,  set  on  a  grade  of  1"  to  the  foot. 
From  these  the  pulp  drops  into  a  box  running  across  the  end  of  the  plate, 
from  whence  it  passes  to  the  vanner.  The  plates  are  scraped  every 
twenty-four  hours,  with  the  exception  of  the  upper  4"  next  the  mortar, 
and  are  dressed  twice  a  day,  using  dilute  cyanide  of  potassium.  Both 
rubbers  and  chisels  are  used  in  scraping  the  plates.  In  cleaning  up  the 
batteries,  which  occurs  once  per  month,  the  headings  are  put  into  a  revolv- 
ing barrel  with  pieces  of  iron  and  ciuicksilver,  and  after  running  several 
hours,  the  contents  are  removed  in  buckets,  the  sand  "boiled  out"  with 
the  hose,  the  dross  skimmed  off,  and  the  quicksilver  strained.  About 
75%  of  the  amalgam  is  saved  in  the  battery.  The  tailings  assay  from 
25  cts.  to  $1   50  per  ton. 

No.  10.  Nevada  County. — The  stamps  weigh  800  lbs.  each,  and  are 
given  a  6"  drop,  100  times  per  minute,  with  a  discharge  varying  from  2" 
to  4";  there  are  no  plates  in  the  battery.  The  ore  passes  over  grizzlies, 
with  bars  H"  apart,  to  a  No.  2  Blake  crusher;  thence  to  the  ore-bin 
that  supplies  the  Challenge  feeders,  which  are  operated  from  the  center 
stamp.  Steel  shoes  and  iron  dies  are  used — the  shoes  lasting,  on  an 
average,  155  days;  the  iron  dies,  70  days.  No.  6  Russian-iron  slot- 
screens  are  used.     The  outside  mortar-plate  is  14"  wide,  with  4''  pitch 


72  CALIFORNIA    GOLD    MILL    PRACTICES. 

to  the  foot,  and  retains  75%  of  the  plate  amalgam.  The  apron  below  is 
4' X  4',  with  a  grade  of  |"  to  the  foot.  Beyond  this  are  12' of  double 
sluice-plates  12"  wide,  and  with  |"  grade  to  the  foot.  Three  sand-boxes 
separate  the  different  apron-plates.  From  the  sluice-plates  the  pulp 
passes  directly  to  the  concentrators.  The  duty  of  the  stamps  is  two 
tons  per  day.  The  tailings  assay  $1  80  to  $2  per  ton.  From  10  to  12 
lbs.  of  quicksilver  per  month  is  used  for  the  40  stamps.  The  plates 
are  scraped  every  day,  and  the  batteries  cleaned  once  a  month,  the 
headings  being  worked  in  a  Knox  pan.  A  weak  solution  of  cyanide  of 
potassium  is  used  in  dressing  the  plates. 

No.  11.  Placer  County. — The  quartz  carries  but  a  small  percentage  of 
sulphurets,  and  is  delivered  from  the  mine  over  an  incline  tramway  to 
two  grizzlies  with  12  bars,  3"  apart,  12'  long,  3"  deep,  and  i"  wide,  set 
on  an  angle  of  45°.  In  front,  below,  and  between  the  grizzlies  is  a 
Blake  crusher,  from  which  the  ore  drops  into  the  bin  that  supplies  the 
Challenge  feeders.  These  are  operated  from  the  center  stamp.  The 
stamps  weigh  750  lbs.  each,  and  drop  5",  90  times  a  minute,  and  the 
discharge  averages  5".  The  screen  is  set  on  a  4"  block,  with  a  5"  plate 
on  the  inside.  The  screen  is  a  No.  10,  slot-punched,  set  with  a  slight 
incline.  Part  of  the  water  for  the  battery  is  supplied  from  a  small 
wooden  trough,  pierced  with  holes  in  front  of  the  screen.  The  outside 
iron  lip  of  the  mortar  is  covered  with  a  silvered  plate.  The  apron,  set 
on  a  grade  of  1|"  to  the  foot,  is  4'  long,  and  is  followed  by  12'  of  sluice- 
plates,  18"  wide.  After  passing  through  a  quicksilver  trap,  the  pulp 
passes  through  a  3"  pipe  to  the  Frue  vanners.  A  tank  of  quicksilver 
is  used  every  three  months,  in  crushing  3,500  tons  of  ore.  The  plates 
are  scraped  every  day  with  rubbers,  and  are  occasionally  dressed  with 
phosphate  of  lime,  or  with  lye.  The  battery  is  cleaned  out  once  a  week, 
and  yields  50%  of  the  amalgam. 

No.  12.  Plumas  County. — The  ore  is  free-milling,  and  contains  about 
li%  of  sulphurets.  It  is  delivered  to  the  Blake  crushers  in  the  mill 
by  an  incline  tramway,  and  the  ore  passes  through  the  bins  to  the 
Challenge  feeders.  The  stamps  weigh  850  lbs.  each,  dropping  8^",  80 
times  per  minute.  The  discharge  varies  from  6"  to  8",  through  No.  8 
diagonal-slot  punched  screens,  with  a  discharging  surface  to  each  battery 
of  45"  in  length  by  6"  in  height.  The  mortar  is  furnished  with  a  lip 
plate  and  a  cast-iron  trough,  which  receives  the  pulp,  also  with  a  5" 
inside  plate.  The  pulp  passes  from  the  trough  to  the  apron  and  sluice- 
plates,  which  have  a  grade  of  1|"  to  the  foot  and  a  length  of  20',  and 
is  then  passed  to  the  concentrators.  Below  the  mill  the  tailings  are 
picked  up  by  outside  parties  and  re-ground  in  arrastras.  The  tailings 
assay  $2  per  ton.  The  loss  of  quicksilver  at  this  mill  is  about  a  flask 
for  every  4,600  tons  crushed.  The  cost  of  milling  does  not  exceed  50 
cents  per  ton  when  using  water-power.  The  plates  are  cleaned  every 
twenty-four  hours.  About  60%  of  the  amalgam  is  derived  from  the 
batteries,  which  are  cleaned  up  once  a  month.  The  headings  are  placed 
in  an  iron  revolving  barrel,  and  the  panning-out  is  done  with  a  batea. 

No.  13.  Plumas  County. — The  ore  is  hauled  to  the  mill  by  wagon, 
and  is  broken  and  fed  by  hand..  The  stamps  weigh  750  lbs.  each,  drop 
5"  to  6",  80  times  per  minute,  with  a  discharge  varying  from  6"  to  8", 


CALIFORNIA   GOLD    MILL    PRACTICES.  iO 

through  a  No.  9  slot-punched,  Russian-iron  screen,  crushing  If  tons  per 
stamp  per  twenty-four  hours.  The  battery  is  supplied  with  an  inside 
plate,  about  6"  wide,  attached  to  the  screen  ;  the  latter  is  set  slightly 
inclined.  The  screen-frame  leaves  about  4"  at  the  upper  end  of  the 
mortar-front  open,  in  front  of  which  and  reaching  nearly  to  the  lip  is  a 
canvas  curtain.  The  apron-plate  is  5'x4-i',  set  on  a  grade  of  1"  in  U"; 
below  the  apron  is  a  drop-box,  from  which  the  pulp  passes  to  the  sluice- 
plates;  these  are  10'  long  by  15"  wide.  The  aprons  are  scraped  every 
day  with  rubbber  belting,  and  the  plate  on  the  screen  is  cleaned  once 
or  twice  a  week.  In  dressing  the  plates,  brine  with  an  addition  of 
sulphuric  acid  is  used.  About  20%  of  the  amalgam  is  saved  in  the 
batteries,  and  about  80%  on  the  plates.  Neither  concentrators  nor  can- 
vas-tables are  used.  One  tank  of  quicksilver  is  used  every  six  months, 
using  twenty  stamps. 

No.  14.  Shasta  County. — The  ores  carries  1^%  of  iron  and  copper 
sulphurets,  besides  free  gold,  averaging  -$9  per  ton.  There  are  30  stamps, 
weighing  850  lbs.  each,  supplied  with  Challenge  feeders,  working  from 
the  second  stamp.  These  stamps  are  hung  and  dropped  somewhat  at 
variance  with  the  usual  custom,  No.  1,  the  end  stamp  on  the  left,  being 
placed  1"  farther  from  the  side  than  is  No.  5,  the  end  stamp  on  the 
right,  and  the  sequence  of  the  drop  is  5,  4,  3,  1,  2;  the  stamps  never 
rising  out  of  the  water.  It  is  claimed  that  by  this  arrangement  a  bet- 
ter swash  is  obtained  in  the  battery.  The  stamps  drop  5",  92  times  per 
minute,  with  a  discharge  of  6"  to  7",  and  crushing  2  tons  per  stamp 
per  twenty-four  hours.  The  mortar  is  supplied  with  front  and  back 
inside  plates.  The  apron-plate  is  4'x4',  set  on  a  grade  of  1^"  to  the 
foot,  followed  by  a  double  set  of  sluice-plates,  16"  wide  and  16'  long, 
with  a  grade  of  1"  to  the  foot.  The  apron-plate  is  kept  rather  wet  with 
mercury  by  frequent  dressing.  Burr-slot  screens,  Nos.  40  and  45,  are 
used.  About  66%  of  the  amalgam  is  derived  from  the  battery.  The 
pulp  is  concentrated  on  four  Triumph  and  ten  Frue  vanners,  and  is  then 
passed  to  two  canvas-platforms,  36'  and  24'  long,  respectively,  and  20' 
wide,  divided  into  sections  2^'  in  width,  covered  with  twill  instead  of 
canvas,  which  is  said  to  give  equally  good  results,  and  is  considerably 
cheaper.  These  tables  have  a  grade  of  1^"  to  the  foot.  The  plates  are 
scraped  once  a  day,  and  the  mill  is  cleaned  up  twice  a  month.  The 
company  chlorinate  their  own  sulphurets,  roasting  in  a  small  two-hearth 
furnace,  with  a  capacity  of  one  ton  per  twenty-four  hours. 

No.  15.  Sierra  County. — On  account  of  to})Ography,  the  ore  has  to  be 
elevated  by  a  lift  to  the  top  of  the  mill.  The  stamps  weigh  8-50  lbs. 
each,  and  drop  5",  80  times  per  minute,  with  a  6"  discharge  through 
No.  7  slot-cut  screens.  The  cams,  bosses,  and  tappets  are  steel;  the 
shoes  and  dies  iron.  The  apron  is  4'x4',  with  a  grade  of  If"  to  the  foot, 
and  is  followed  by  a  double  sluice-plate,  16"  wide,  12'  long,  and  })itched 
1:^"  to  the  foot.  The  plates  are  not  scraped  at  regular  intervals;  in 
dressing  them,  lye  is  used  occasionally.  The  plate  on  the  screen, 
6"x52",  is  cleaned  every  other  day.  About  86%  of  the  amalgam  is 
saved  in  the  battery,  and  the  tailings  only  show  a  trace  of  gold.  John- 
ston concentrators  receive  the  pulp  from  the  plates;  these  concentrators 
are  run  with  110  to  112  side-stroke?  per  minute,  the  l?elt  revolving  once 
in   seven  minutes.     The   waste  from    the  concentrators  is  forced  to  a 


74  CALIFORNIA   GOLD   MILL    PRACTICES. 

higher  level  by  an  "ejector,"  and  then  passes  through  a  pointed  box. 
The  heavy  material  is  then  passed  through  a  series  of  drop-boxes  and 
discharged  into  the  river. 

No.  16.  Sierra  County. — The  ore  carries  a  considerable  amount  of 
clay,  and  is  delivered  to  the  mill  over  an  incline  track  to  a  Blake 
crusher.  The  stamps  weigh  850  lbs.  each,  and  make  75  to  78  drops  of 
6"  per  minute,  with  a  discharge  varying  from  7"  to  9",  using  a  No.  10 
slot-cut  screen.  The  inside  of  the  mortar  is  furnished  with  front  and 
back  plates,  the  former  8",  the  latter  4"  wide.  Cast-iron  shoes  and  dies 
are  used,  crushing  1^  tons  to  the  stamp  per  day.  The  order  in  which 
the  stamps  drop  is  1,  5,  2,  4,  3.  The  apron-plate  is  the  width  of  the 
mortar,  is  6'  long,  and  is  set  to  a  grade  of  2^"  to  the  foot,  followed  by  12' 
of  sluice-plates,  14"  wide.  As  there  are  but  few  sulphurets,  no  concen- 
trators are  in  the  mill.  The  apron  and  sluices  are  dressed  every  day, 
but  only  scraped  once  a  month;  cyanide  of  potassium  is  used  in  dress- 
ing the  plates.  The  battery  is  cleaned  once  a  month.  About  5  lbs.  of 
quicksilver  is  used  to  every  1,500  tons.  About  70%  of  the  amalgam  is 
obtained  from  the  battery. 

No.  17.  Tuolumne  County. — This  mill  of  10  stamps  crushes  quartz 
containing  little  or  no  free  gold,  but  with  3  per  cent  of  sulphurets,  chiefly 
iron.  The  stamps  weigh  1,000  lbs.  each  (fed  by  self-feeders),  working 
at  96  drops  of  6",  crushing  2\  tons  per  stamp.  Chrome  steel  shoes  and 
dies  are  used,  which  wear  about  1"  per  week.  No.  30  brass  wire  screens 
are  used,  the  screen  having  a  slight  inclination,  10°.  There  are  no  plates 
used  on  the  inside  of  the  battery,  and  only  one  apron-plate,  4^'x6',  to 
each  five  stamps,  which  is  dressed  daily.  It  is  set  to  a  grade  of  If"  to 
the  foot.  Nearly  all  of  the  amalgam  is  derived  from  this  apron.  The 
pulp  passes  from  the  aprons  through  a  series  of  troughs  to  four  Frue 
concentrators  with  corrugated  belts,  using  a  large  amount  of  water. 
These  are  succeeded  b}^  wooden  troughs,  8"  wide  at  top,  spreading  to  16", 
which  divide  into  three  troughs,  carrying  equal  amounts  of  pulp,  thinned 
by  adding  3  miner's  inches  of  clear  water  above  the  forks.  These  deliver 
into  a  V-trough  running  at  the  head  of  a  canvas-platform,  divided 
into  twelve  sections,  22"  wide  and  75'  long,  set  on  a  grade  of  l^"to  the 
foot.  These  tables  are  covered  with  No.  7  duck,  which  lasts  90  days. 
The  V-trough  has  extending  over  its  entire  length  a  square  8"  trough, 
for  clear  water.  The  pulp  flows  from  the  V-trough  through  1"  auger- 
holes  (two  to  each  section  of  the  canvas),  supplied  with  wooden  plugs 
to  regulate  the  flow  of  the  pulp,  the  clear-water  trough  being  similarly 
supplied.  Every  half  hour  the  flow  of  the  pulp  is  arrested  on  a  section, 
while  the  flow  of  clear  water  is  continued  until  the  lighter  sands  are 
washed  off,  leaving  the  sulphurets  on  the  canvas.  The  flow  from  the 
tables  is  delivered  into  V-boxes  running  across  the  end  of  the  canvas- 
platform,  with  a  grade  from  the  outer  edges  to  the  center,  and  delivered 
to  a  second  canvas-table  trough,  where  it  undergoes  a  similar  treatment. 
After  removing  the  lighter  sands  from  the  upper  platform,  a  sheet-iron 
pan  is  placed  below  the  end,  which  extends  to  a  separate  trough,  into 
which  the  sulphurets  adhering  to  the  canvas  are  swept  with  the  aid 
of  the  flowing  clear  water,  and  conveyed  to  a  settling-tank  divided 
into  two  sections  in  such  a  way  that  when  one  section  is  filled,  the 
sulphurets    are  run  into  the  second    section,  allowing  the  first  to  be 


CALIFORNIA   GOLD    MILL    PRACTICES. 


shoveled  out,  each  section  being  treated  consecutively.  When  No.  1  is 
being  swept,  No.  2  has  the  pulp-flow  shut  off,  making  the  operation 
continuous.  After  sweeping  down  a  section,  the  plugs  from  the  pulp 
trough  are  removed  and  the  clear  water  shut  off,  permitting  the  concen- 
tration to  be  renewed.  It  requires  the  attention  of  two  persons,  night 
and  day,  to  attend  to  these  two  platforms.  Everything  but  the  sweep- 
ings pass  over  the  second  canvas-platform,  and  then  go  to  waste.  The 
sweepings  from  the  second  table  are  treated  in  a  manner  similar  to  those 


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/9-isi7ia    ii/M£  sfTrtiMe  m/v/fs 
16  Si/At£    s£TTi//ve  r/toc/t:Ms 


Fig.  50. 

from  the  upper  one.  Accessory  to  these  two  sulphuret  settling-tanks  are 
two  large  slime  settling-tanks;  these  are  divided  into  twenty  sections,  2' 
square,  20'  long,  divided  from  each  other  by  2"  plank  extending  entirely 
across  the  tank.  Within  2'  of  the  ends^  on  alternate  sides  of  these 
divisions,  slots  4"  deep  and  2'  wide  are  cut  to  permit  the  water,  which 
is  clouded  with  the  fine  slimes,  to  pass  from  one  division  to  the  other. 
At  the  end  farthest  from  the  entrance,  the  water  (still  somewhat 
clouded)  runs  to  waste.  The  slime  water  from  the  first  settling-tank 
passes  through  the  second.     The  sulphuret  settling-tanks  are  shoveled 


76  CALIFORNIA   GOLD    MILL    PRACTICES. 

out  every  few  days,  while  the  slime  settling-tanks  remain  undisturbed 
for  months.  The  material  from  the  vanners,  upper  and  lower  settling- 
tanks,  and  sometimes  from  the  slimes,  is  mixed  by  weight  before  going 
to  the  chlorination  works.  There  are  2,400  sq.  ft,  of  canvas-tables  and 
5,000  sq.  ft.  of  settling-floor. 

No.  18.  Tuolumne  County. — This  mill  is  working  on  quartz  carrying 
both  free  gold  and  sulphurets.  The  ore  is  delivered  from  the  mine  at 
the  top  of  the  mill,  into  a  general  ore-bin,  for  the  entire  40  stamps,  after 
passing  through  the  rock-breaker.  The  bin  has  a  capacity  of  650  tons, 
and  delivers  the  ore  into  the  self-feeders  direct.  The  stamps  weigh  850 
lbs.  each,  and  steel  shoes  and  dies  are  used.  Each  stamp  has  its  sepa- 
rate guide,  made  of  two  blocks  of  hard  maple,  fitted  together  and  bored 
through  to  receive  the  stem.  The  front  block  is  first  put  in  place,  the 
stem  set  in,  and  the  rear  block  dropped  in  behind  a  cast-iron  piece, 


MOl^ABLE  APffOA/ 


Fig.  5L 

which  is  secured  by  wooden  wedges  driven  in  from  above,  so  that  when 
required  it  can  easily  be  removed.  The  pulp  from  the  battery  falls  over 
a  9"  silvered  plate,  the  width  of  the  mortar,  into  a  box  12"  square,  sup- 
plied with  six  1"  holes,  8"  apart,  near  the  front  lower  edge,  that  permit 
the  pulp  to  flow  onto  a  4'x  5'  silvered  plate,  divided  in  two  parts  by  a 
wooden  strip  down  the  center.  The  fall  from  the  box  to  the  plate  is  oV' . 
The  apron-plate  is  mounted  on  a  carriage,  which  can  be  pushed  back, 
giving  access  to  the  battery,  the  4"  grooved  wheels  in  front  running  on  a 
half-round  iron  strip  placed  on  the  sides  of  the  lower  plate-frame.  From 
the  movable  apron  the  pulp  passes  over  12'  of  plates,  divided  into  three 
4'  sections,  with  a  dividing  strip  down  the  center.  Sixteen  concentrators 
are  used. 

No.  19.  Tuolumne  County. — This  mill  presents  some  peculiarities  in 
its  construction.  There  are  10  stamps  of  850  lbs.  each,  with  steel  shoes 
and  dies.  The  stamps  are  given  100  drops  per  minute,  dropping  4^", 
Avith  only  2^"  discharge  to  commence  on,  through  a  No.  50  brass-wire 
screen.  The  rock-breaker  (Wheeler  pattern)  and  ore-bin  are  set  on  a 
rock  foundation,  the  frames  being  entirely  disconnected  from  the  rest  of 
the  building,  to  counteract  the  vibratory  motion  of  the  crusher.  In 
placing  the  mortar-block  and  mortar,  the  space  around  the  block  was 
filled  in  with  concrete,  and  a  double  thickness  of  tanned  belting  laid 
between  the  block  and  the  mortar,  after  which  a  fire  was  built  in  the 
latter  until  it  settled  into  the  belting.  The  Avear  of  the  shoes  and  dies 
is  about  1"  per  month,  and  the  duty  of  the  stamps  1|  tons  per  stamp. 
When  the  dies  are  partially  worn,  a  2"  iron  plate  is  placed  under  them, 
to  maintain  a  regular  discharge.  The  inside  of  each  mortar  is  provided 
with  cast-iron  side  plates  and  a  sheet-iron  covered  board  at  the  back,  to 
prevent  wear  on  the  mortar.  The  apron-plates  are  set  12"  out  from  the 
mortar.     The  pulp  from  the  battery  passes  over  a  9"  plate  into  double- 


CALIFORNIA    GOLD    MILL    PRACTICES.  77 

pointed  boxes  of  iron,  bolted  on  tbe  front  of  the  mortar,  and  thence 
through  a  couple  of  2"  pipes  to  a  spreader  and  to  the  silver-plated 
apron.  The  apron  is  followed  by  double  sluice-plates,  each  2'  wide  and 
10'  long,  all  set  on  a  grade  of  1^"  to  the  foot.  Two  thirds  of  the  amal- 
gam is  obtained  from  the  battery.     No  concentrators  are  used. 


SPECIFICATIONS  FOR  A  FORTY-STAMP  GOLD  MILL  (WATER 

POWER).* 

MACHINERY. 

Water  Wheels  and  Pulleys. — One  water  wheel,  6'  in  diameter,  to  drive 
the  battery;  the  wheel  to  be  supplied  with  a  shaft,  boxes,  collars,  gate, 
and  nozzle,  automatic  governor,  and  a  pulley  36"  in  diameter,  grooved 
for  1^"  manilla  ropes. 

One  driving  pulle}',  12'  in  diameter. 

One  idler  pulley,  48"  inches  in  diameter,  grooved  for  one  1^"  rope,  and 
fitted  with  shaft  and  boxes. 

One  slack-tightener  pulley,  48"  in  diameter,  grooved  for  one  1^"  rope, 
and  fitted  with  shaft,  boxes,  carriage,  track,  and  counterbalance  weight. 

The  rope  for  transmission  is  to  be  put  on  in  one  piece,  passing  around 
the  idler  and  slack-tightener  (which  are  to  be  set  on  an  angle  in  such  a 
way  that  they  will  take  the  rope  from  one  side  of  one  of  the  main  pulleys 
and  pass  it  on  to  the  opposite  side  of  the  other  pulley),  thereby  making 
but  one  splice  in  the  whole  rope,  which  will  be  kept  in  constant  tension 
by  the  slack-tightener. 

One  wheel,  4'  in  diameter,  to  drive  the  rock-breakers;  the  wheel  to 
be  supplied  with  a  shaft,  boxes,  collars,  gate,  and  nozzle,  and  a  pulley 
34"  in  diameter,  grooved  for  one  1^"  manilla  rope. 

One  driving  pulley,  60"  in  diameter. 

One  idler  pulley,  30"  in  diameter,  grooved  for  one  1-|"  rope,  and  fitted 
with  shaft  and  boxes. 

One  slack-tightener  pulley,  30"  in  diameter,  grooved  for  one  l-k"  rope, 
and  fitted  with  shaft,  boxes,  carriage,  track,  and  counterbalance  weight; 
rope  to  be  put  on  similar  to  that  for  the  battery. 

One  wheel,  36"  in  diameter,  to  drive  the  concentrators;  the  wheel  to 
be  supplied  with  shaft,  boxes,  collars,  gate,  and  nozzle,  automatic  gov- 
ernor, and  a  pulley  16"  in  diameter,  grooved  for  one  1"  manilla  rope. 

One  driving  pulley,  48"  in  diameter. 

Forty-Stamp  Battery;  stamps  to  weigh  850  to  900  lbs.  each,  arranged 
to  run  in  eight  batteries  of  five  stamps  each,  by  belts  and  friction  clutch 
pulleys  from  battery  line  shaft. 

Eight  high  cast-iron  Mortars,  single  discharge,  each  to  weigh  about 
5,000  lbs.;  to  be  planed  all  over  the  bottom,  and  faced  where  the  apron 
joins  on;  eight  holes  to  be  accurately  cored  in  the  base  for  1^"  anchor 
bolts.  Each  mortar  to  have  five  cast-iron  linings.  The  aggregate 
weight  of  these  linings  is  about  500  lbs.  per  mortar. 

Eight  cast-iron  Aprons,  to  be  faced  where  they  join  on  to  the  mortars, 
and  fastened  in  place  with  |"  bolts. 

♦  From  the  Vlllth  Report  of  State  Mineralogist,  1888,  p.  728. 


78  CALIFORNIA    GOLD    MILL    PRACTICES. 

Eight  sugar  pine  Screen  Frames,  to  have  iron  facings  put  on  the  ends 
where  the  keys  bear  against  them;  the  edges  to  be  titled  with  dowel- 
pins  to  join  them  to  the  inside  plate-block. 

Sixteen  inside  Plate- Blocks,  two  sets,  one  to  be  6"  high,  and  the  other 
to  be  4"  high;  to  be  well  fitted  into  the  mortars,  and  to  have  plates 
fitted  and  fastened  on  with  brass  screws;  blocks  to  be  bolted  together  to 
keep  them  from  splitting,  and  to  be  fitted  with  iron  facings  where  the 
keys  bear  against  them,  and  well  fitted  to  the  screw  frames. 

Eight  brass  wire  Screens,  No.  30  mesh,  to  be  fastened  on  to  the  screw- 
frames  with  copper  tacks. 

Sixteen  gilt-headed  End  Keys,  for  screen  frames,  to  be  well  fitted  in 
place. 

Sixteen  Bottom  Keys,  for  screen  frames,  to  be  well  fitted  in  place. 

Sixty-four  Foundation  Bolts,  for  mortars,  to  be  l-g"  in  diameter  by  30" 
long,  with  hexagon  nuts  on  the  top  ends  and  steel  keys  in  the  bottom 
ends. 

Sixty-four  wrought-iron  Washers,  4"x4"x|",  for  bottom  ends  of  foun- 
dation bolts. 

Eight  sheets  of  Rubber,  i"  thick  by  30"  by  60",  for  mortar  foundation. 
Mill  blankets  tarred  may  be  used  in  place  of  rubber. 

Forty  chrome  steel  or  cast-iron  Dies,  9"  in  diameter  by  7"  high,  with 
square  base  well  fitted  into  the  mortars,  10"  from  center  to  center. 

Forty  chrome  steel  Shoes,  9"  in  diameter  by  8"  high,  with  tapered 
shank  3f"  in  diameter  at  top  end,  4|"  in  diameter  at  bottom  end,  by  5" 
long,  to  fit  into  the  stamp-heads  by  being  covered  with  dry,  hard  pine 
■f"  thick;  this  being  driven  in  by  being  allowed  to  drop  a  few  times  on 
the  bare  die. 

Forty  chrome  steel  Stamp-Heads,  9"  in  diameter  by  17"  long,  with  a 
conical  socket  cored  into  the  lower  end,  4"  in  diameter  at  inner  end 
and  5^"  in  diameter  at  the  outer  end,  and  5^"  deep,  and  a  conical  socket 
cored  and  actually  bored  out  to  fit  the  tapered  end  of  the  stamp  stem, 
2|"  in  diameter  at  inner  end,  and  3^"  gauge  at  the  outer  end,  by  6" 
deep.  Transverse  rectangular  keyways  are  to  be  cored  through  the 
stem-head,  l"x2-|",  for  loosening  the  shoes  and  stems. 

Two  steel  Loosening  Keys,  ■^"  thick  by  1"  at  the  point  (2"  at  the  head) 
by  18"  long,  for  loosening  the  shoes  and  stems. 

Forty  best  refined  iron  or  mild  steel  Stems,  turned  perfectly  true,  full 
length,  3i"  gauge  by  14'  long,  to  be  tapered  on  both  ends  to  accurately 
fit  the  stamp-heads.     Each  stem  weighs  about  360  lbs. 

Forty  chrome  steel,  double-faced  Tappets,  9"  in  diameter  by  11"  long, 
with  a  steel  gib  and  two  steel  keys  accurately  fitted  in  place;  both  faces 
to  be  turned  true;  tappets  to  be  bored  with  the  gibs  in  place  to  accu- 
rately fit  the  stems,  and  to  be  counter-bored  opposite  the  gibs  by  mov- 
ing tlie  center  i"  aw-ay  and,  with  diameter  ^"  less  than  the  bore,  taking 
a  cut  "I"  deep.     Each  tappet  weighs  112  lbs. 

Eight  Upper  and  eight  Lower  Guides,  with  cast-iron  frames;  guide- 
blocks  to  be  made  of  good,  dry  maple  timber  and  well  fitted  in  place; 
the  guides  may  also  be  made  entirely  of  wood. 


CALIFORNIA    GOLD    MILL    PRACTICES.  79 

Four  extra  quality,  mild  steel  Cam-Shafts,  turned  true  full  length, 
5^"  gauge  diameter  by  14'  long;  key-seated  for  cams  and  pulley;  key- 
seats  must  not  run  through  the  bearings. 

Ten  heavy  Corner  Boxes,  bV'  gauge  bore;  eight  of  them  to  be  12" 
long,  and  two  to  be  20"  long;  all  of  them  to  be  planed  all  over  the  bot- 
toms and  backs,  and  furnished  with  bolts  1"  in  diameter,  to  fasten  them 
to  the  battery  frame. 

Forty  double-armed,  chrome  steel  Cams — twenty  right  and  twenty 
left  hand — to  be  made  29"  long  over  all,  the  hub  to  be  11"  in  diameter 
and  5^"  through  the  bore;  the  lifting  faces  to  be  2V'  wide,  and  ground 
smooth;  the  hubs  to  be  bored  to  fit  the  shaft  accurately,  and  properly 
key-seated  and  fitted  with  steel  keys,  and  each  marked  to  their  respect- 
ive places,  giving  them  a  combination  as  follows:  Counting  from  the 
left-hand  side,  when  facing  the  battery,  throughout  the  full  ten  stamps 
of  each  cam-shaft,  No.  1  cam  will  drop  its  stamp  first;  then  Nos.  8,  4, 
10,  2,  7,  5,  9,  3,  and  6  consecutively.  This  is  the  order:  1,  4,  2,  5,  3. 
Each  cam  weighs  about  158  lbs.  The  curve  of  the  face  of  the  cam  is 
the  involute  of  a  circle,  usually  slightly  modified. 

Four  pairs  of  cast-iron  double  Sleeve  Flanges,  for  wood  pulleys; 
flanges  to  be  36"  in  diameter,  and  14"  through  the  bore;  to  be  turned 
all  over  the  inside,  where  they  fit  on  the  wood;  the  outside  flange  is  to 
be  bored  and  fitted  to  the  sleeve  and  fastened  with  a  gib-headed  steel 
key;  the  hub  to  be  bored  and  fitted  to  the  cam-shaft  and  fastened  with 
a  steel  key. 

Four  Wood  Pulleys,  72"  in  diameter  by  17"  face;  to  be  made  of  best 
kiln-dried  sugar  pine,  and  all  joints  to  be  filled  with  white  lead  in  oil; 
the  cast-iron  flanges  to  be  well  fitted  on  and  bolted  with  twelve  f"  bolts. 

Eight  wrought-iron  Collars,  for  cam-shaft,  oV'  bore,  fitted  with  two 
steel  set-sere w'S  in  each. 

Eight  wrought-iron  Jack-Shafts,  3"  in  diameter  by  60"  long;  black 
finish. 

Sixteen  cast-iron  Jack-Shaft  Side  Brackets,  with  four  lag-screws,  | " 
by  6",  for  each,  to  fasten  them  in  place. 

Forty  open  Latch  Sockets,  lined  with  leather. 

Forty  wood  Finger-bars,  to  be  fitted  and  bolted  to  the  above  sockets, 
and  furnished  with  wrought-iron  caps  and  handles. 

A  complete  set  of  Water-Pipes  for  a  battery  of  forty  stamps,  with  all 
fittings,  cocks,  and  connections. 

Bolts  and  Washers  for  Battery  Frame. — Six  brace  rods,  l^"x2o',  7" 
between  two  nuts;  6  brace  rods,  l^"xl2',  6"  between  two  nuts:  26  bolts 
for  mudsills,  l"x30";  24  bolts  for  yokes,  l"x28";  24  bolts  for  vokes, 
l"x52";  48  bolts  for  guide  girts,  l"x32";  4  bolts  for  knee  beam,  l"x28"; 
36  splice  bolts  for  mudsills, -I",  16"  between  head  and  nut;  12  splice 
bolts  for  tail  girt,  |",  9V'  between  head  and  nut;  32  bolts  for  mortar- 
blocks,  1",  59"  from  point  to  point;  64  bolts  for  mortar-blocks,  1",  65" 
from  point  to  point;  24  joint  bolts  for  posts,  1",  35"  between  two  nuts; 
6  joint  bolts  for  knee  posts,  1",  45"  between  two  nuts;  6  joint  bolts  for 
knee  posts,  1",  35"  between  two  nuts;  24  joint  bolts  for  knee  beams,  1", 


80  CALIFORNIA   GOLD    MILL    PRACTICES. 

43"  between  two  nuts;  10  jointlbolts  for  tail  girts,  1",  21"  between  two 
nuts;  24  cast-iron  washers  for  1^"  rods;  514  cast-iron  washers  for  1" 
bolts;  72  cast-iron  washers  for  |"  bolts;  24  cast-iron  washers  for  |" 
bolts;  40  sheet-iron  washers,  3^"  square  by  i"  thick,  for  1"  joint  bolts. 

Battery  Line  Shafting  and  Pulleys. — One  shaft,  5^"  gauge  by  18'  long, 
properl}'  key-seated;  one  shaft,  5"  gauge  by  15'  6"  long,  properly  key- 
seated;  one  shaft,  5"  gauge  by  17'  long,  properly  key-seated;  one  shaft, 
4"  gauge  by  17'  long,  properly  key-seated;  two  shafts,  3"  gauge  by 
10'  6"  long,  properly  key-seated;  two  face  couplings,  5"  gauge,  properly 
fitted  and  keyed  in  place;  one  face  coupling,  4"  gauge,  properly  fitted 
and  keyed  in  place;  two  face  couplings,  3"  gauge,  properly  fitted  and 
keyed  in  place;  two  babbitted  boxes,  5^"  gauge;  three  babbitted  boxes, 
5"  gauge;  two  babbitted  boxes,  4"  gauge;  two  babbitted  boxes,  3"  gauge; 
all  of  the  above  boxes  to  be  made  of  the  same  height,  planed  all  over 
the  bottoms,  with  drip  cups  cast  on  to  the  sides,  and  furnished  with 
suitable  bolts  to  fasten  them  to  the  16"  battery  knee  beams;  two  collars 
for  5-^"  shafting,  with  two  steel  set-screws  in  each;  four  friction  clutch 
pulleys,  48"  in  diameter  and  16^"  face,  complete,  with  levers  and  con- 
nections; pulleys  to  be  fitted  to  line  shaft  in  their  proper  places,  with 
phosphor-bronze  bushings,  the  drivers  to  be  properly  keyed  on  with 
steel  keys;  one  pulley,  6'  in  diameter,  grooved  for  three  1^"  manilla 
ropes,  pulley  to  be  well  balanced  and  keyed  to  the  shaft  with  a  steel  key. 

Water-Pipes. — Sufficient  3"  pipes  and  fittings  to  connect  battery  pipes 
with  feed-water  tanks. 

Traveling  Hoist. — One  traveling  crab,  with  track-iron  and  rails,  to 
extend  full  length  of  battery. 

One  2-ton  Weston's  differential  chain-block. 

Ore-Feeders. — Eight  Challenge  self-feeders,  complete,  for  batteries, 
with  all  connections. 

Ore-Bin  Gates. — Eight  ore-bin  gates,  18"x24",  for  fine  ore,  with  guides, 
racks,  pinions,  shafts,  boxes,  hand-wheels,  and  bolts. 

Three  ore-bin  gates,  24"x36",  for  coarse  ore,  with  guides,  racks,  pinions, 
shafts,  boxes,  hand-wheels,  and  bolts. 

Sluices  and  Aprons. — Eight  cast-iron  aprons,  54"  wide  by  56"  long, 
to  be  fitted  under  the  lip  of  the  mortar  apron. 

Eight  silver-plated  copper  plates,  54"x56"x-|",  to  be  made  of  best 
Lake  Superior  copper,  and  to  have  one  ounce  of  silver  per  square  foot; 
plates  to  be  fitted  into  the  cast-iron  aprons,  and  fastened  by  strips  of 
wood  on  the  sides,  which  are  bolted  to  the  sides  of  the  apron. 

Eight  cast-iron  sluices,  54"  wide  by  12' long,  to  be  made  into  two  sections 
and  bolted  together  by  flanges,  the  lower  section  to  have  a  quicksilver 
trap  or  trough  cast  on  to  the  end,  extending  the  full  width  of  the  sluice, 
and  to  have  a  connection  made  for  a  2"  pipe  to  conduct  the  pulp  to  the 
dividing  tanks,  and  thence  to  the  concentrators. 

Twenty-four  silver-plated  copper  plates,  54"x48"x^",  to  be  made  of 
best  Lake  Superior  copper,  and  to  have  one  ounce  of  silver  per  square 
foot;  plates  to  be  fitted  into  the  sluices,  overlapping  at  the  joints,  and 
to  be  fastened  in  place  in  the  same  manner  as  those  in  the  apron. 

There  are  to  be  eight  silver-plated  copper  shaking-tables,  one  for  each 
battery,  placed  below  the  apron-plates.     These  tables  consist  of  a  light 


CALIFORNIA    GOLD    MILL    PRACTICES.  81 

iron  framework  suspended  upon  movable  springs.     This  table  is  given 
a  longitudinal  oscillation  by  means  of  eccentrics. 

Dividing  Tanks  and  Pulp  Pipes. — Eight  cast-iron  dividing  tanks,  10" 
long  by  8"  wide  by  6"  deep,  with  2"  pipe  connection  in  one  end  and  two 
1^"  pipe  connections  in  the  other  end,  each  to  have  a  wooden  swinging 
tongue  put  in  so  as  to  direct  the  pulp  to  either  of  the  H"  pipes,  or  a 
part  to  the  one  and  a  part  to  the  other.  The  tanks  are  to  be  connected 
with  the  sluices  by  2"  pipes,  and  with  the  concentrators  by  li"  pipes. 

Inside  Plates  and  Blocks. — Three  wooden  blocks  for  each  mortar,  to  be 
3",  44",  and  6"  high,  respectively,  to  be  fitted  into  the  mortars  under  the 
screw  frames;  each  block  to  have  iron  facings,  fitted  in  flush  and 
screwed  on  where  the  keys  come,  and  to  have  a  silver-plated  copper 
plate  bent  to  the  proper  shape  and  screwed  on  with  silver-plated  brass 
screws;  the  copper  plates  to  be  made  of  best  Lake  Superior  copper, 
6"x50"xyV,  and  to  have  one  ounce  of  silver  per  square  foot. 

Concentrators  and  Shafting. — Sixteen  endless  belt  concentrators,  com- 
plete, with  water-pipes  and  fittings  to  connect  with  supply  tanks.  All 
Bulphuret  tanks,  complete,  to  be  made  of  good  redwood  lumber. 

One  piece  of  shafting,  2-i"xl6';  six  pieces  of  shafting,  2"xl6';  three 
pieces  of  shafting,  2"xl0';  eight  face  couplings,  2";  four  babbitted 
boxes,  2^",  with  bolts  for  8'  timber;  eighteen  babbitted  boxes,  2",  with 
bolts  for  8"  timber;  two  collars,  2^",  with  steel  set-screws;  two  collars, 
2",  with  steel  set-screws;  one  pulley,  48"  in  diameter,  grooved  for  one 
1"  rope,  and  properly  fitted  and,  keyed  with  a  steel  key  to  2^"  shaft; 
two  pulleys,  6"  face  by  36"  in  diameter,  properly  fitted  and  keyed  with 
steel  keys  to  the  2"  shaft;  sixteen  pulleys,  4"  face  and  10"  in  diameter, 
properly  fitted  and  keyed  with  steel  keys  to  the  2"  shaft;  sixteen  loose 
pulleys,  4"  face  by  10"  in  diameter,  properly  fitted  to  the  2"  shaft;  six- 
teen colhirs,  with  steel  set-screws  for  same. 

Rock-Breakers  and  Shafting. — Two  rock-breakers,  9"x  15";  one  piece 
shafting,  4"x  16';  one  piece  shafting,  3^"x  16';  one  piece  shafting,  3"x  16'; 
one  face  coupling,  o\";  one  face  coupling,  3";  three  babbitted  boxes,  4", 
with  bolts  for  10"  timber;  two  babbitted  boxes,  3^",  with  bolts  for  10" 
timber;  two  babbitted  boxes,  3",  with  bolts  for  10"  timber;  two  collars, 
4",  with  steel  set-screws;  one  pulley,  48"  in  diameter,  grooved  for  1"  and 
1,J"  manilla  rope,  and  properly  fitted  and  keyed  to  the  4"  shaft,  with  a 
steel  key;  three  pulleys,  20"  straight  face  by  20"  in  diameter,  properly 
fitted  and  keyed  to  the  shafting. 

Clean-up  Barrel. — One  clean-up  barrel,  24"  inside  diameter  by  -^8" 
inside  length,  to  be  made  of  cast-iron  1^"  thick,  with  two  discharge 
openings,  5^"  in  diameter,  in  the  sides  diametrically  opposite  each  other, 
the  heads  and  discharge  doors  to  be  accurately  fitted;  journals  to  be  4" 
gauge,  cast  on  to  the  heads;  one  tight  and  one  loose  pulley,  7"  face  by 
30"  in  diameter;  two  babbitted  boxes,  4"  gauge;  one  driving  pulley,  6" 
in  diameter  by  14"  face. 

Batea. — One  batea,  48"  in  diameter,  with  gears  and  hangers  complete, 
and  tight  and  loose  pulleys,  AV'  face  by  16"  in  diameter;  one  driving 
pulley,  9"  face  by  21"  in  diameter. 

Machinery  for  Clean-up  Room. — One  clean-up  pan,  24"  inside  diameter, 
with  tight  and  loose  pulleys. 

6 GMP 


82  CALIFORNIA    GOLD    MILL    PRACTICES. 

One  driving  pulley,  8"  face  by  16"  in  diameter. 

One  cast-iron  washing-tank,  24"  by  30"  b}'-  24"  deep,  with  three  pipe 
connections  for  drawing  off  water. 

One  cast-iron  washing-tank,  30"  by  36"  by  24"  deep,  with  three  pipe 
connections  for  drawing  off  water. 

One  cast-iron  washing-tank,  30"  by  54"  by  30"  deep,  with  three  pipe 
connections  for  drawing  off  water. 

One  marble  top,  complete,  for  washing-tanks. 

One  side  washstand,  with  pipes  and  fittings. 

All  pipes  and  fittings  necessary  to  bring  water  to  the  clean-up  pan 
and  washing-tanks. 

Retort  and  Melting  Furnace. — One  retort,  10"x36",  inside  dimensions, 
with  amalgam  trays,  condenser,  catch  tank,  furnace  front,  bearers,  bars, 
smokestack,  and  base  plate,  guy  rods,  dampers,  binders,  and  all  pipes 
and  fittings  to  bring  water  to  the  condenser. 

One  cast-iron  melting  furnace,  complete,  with  doors,  grate-bars,  bearers, 
cast-iron  shell,  and  damper. 

Two  bullion  molds  for  500  and  750  ounces. 

Four  black-lead  crucibles.  No.  16,  with  covers. 

One  crucible  tongs  for  No.  16  crucible. 

One  skimmer  for  bullion. 

Transmission  Ropes  and  Belts. — Six  hundred  feet  best  manilla  or 
cotton  rope,  1^"  in  diameter,  to  drive  battery  line  shaft. 

Two  hundred  and  fifty  feet  best  manilla  rope,  1^"  in  diameter,  to 
drive  rock-breaker  line  shaft. 

One  hundred  and  fifty  feet  best  manilla  rope,  1"  in  diameter,  to  drive 
concentrator  line  shaft. 

Two  hundred  feet  best  rubber  belting,  16"  by  5-ply,  for  batteries. 

One  hundred  and  eighty  feet  best  rubber  belting,  10"  by  4-ply,  for 
rock-breakers. 

Thirty-two  feet  best  rubber  belting,  7"  by  4-ply,  for  clean-up  barrel. 

Sixty-five  feet  best  rubber  belting,  6"  by  4-ply,  for  batea. 

Thirty  feet  best  rubber  belting,  6"  by  4-ply,  for  concentrator  shafting. 

Four  hundred  and  twenty  feet  best  rubber  belting,  3"  by  4-ply,  for 
concentrators. 

Thirty  feet  best  rubber  belting,  3"  by  4-ply,  for  clean-up  pan. 

BUILDINGS,    AND    ERECTION    OF    MILL,    ETC. 

Stonework. — All  foundations  and  retaining  walls  to  be  built  of  large 
stone,  properly  banded,  and  well  laid  in  cement  mortar,  composed  of 
ten  parts  good,  clear  sand,  two  parts  good  quality  of  lime,  and  one  part 
best  Portland  cement,  special  care  being  taken  to  keep  all  dirt  or  clayey 
material  excluded;  all  exposed  faces  of  retaining  walls  to  be  well  pointed 
up  and  finished  with  the  same  material. 

Ore-Bins. — Mudsills  to  be  made  of  12"xl4"  timbers,  laid  flatwise; 
foundation  posts  to  be  made  of  14"xl4"  timbers;  sills,  posts,  and  caps 
for  ore-bins  proper  to  be  made  of  12"xl2"  timbers,  the  posts  to  be  boxed 
1"  into  the  sills  and  caps;  braces  for  incline  bottom,  to  be  made  of 
10"xl2"  timbers;  supporting  braces  to  be  made  of  8"xl2"  timbers.  All 
planking  to  be  3"  thick  and  lined  throughout  with  1"  boards,  to  break 
joints  over  the  planks. 


CALIFORNIA    GOLD    MILL    PRACTICES.  83 

Battery  Frame. — Mudsills  to  be  made  of  14"xl6"  sugar  pine,  or  good 
yellow  pine  free  from  sap;  to  be  well  bedded  in  concrete,  which  must 
be  put  on  the  clean  bedrock.  Linesills  to  be  made  of  12"xl6"  and 
20"xl6"  sugar  pine  or  yellow  pine,  of  good  quality,  to  be  well  bolted  down 
to  the  mudsills. 

Mortar-blocks  to  be  made  of  two  pieces  each,  to  be  30"  thick  and  wide 
enough  to  fill  space  between  the  linesills  and  battery  posts;  all  to  be 
sized  and  well  fitted.  The  timbers  for  mortar-blocks  are  to  be  accurately 
fitted  together  and  secured  with  six  1"  bolts,  and  two  oak  keys,  4"  wide 
by  5"  thick  at  the  point  and  6"  at  the  head.  Keys  to  be  accurately 
fitted  and  firmly  driven.  Blocks  to  be  sized  and  finished  above  the 
floors. 

Yokes  to  be  made  of  10"xlO"  timber,  well  fitted  and  bolted  to  the 
linesills  and  battery  posts. 

Battery  posts  to  be  made  of  r2"x24:"  and  20"x24",  good  quality  pine 
timber,  to  be  dressed  all  over,  and  bolted  down  to  the  linesills  with  1" 
joint  bolts,  the  large  posts  to  be  made  with  double  tennon  on  the  bottom. 
The  knee  beams  to  be  made  of  12"xl6"  timber,  dressed  all  over.  The 
knee  posts  to  be  made  of  12"xl6"  timber,  dressed  all  over.  The  stringer 
on  top  of  the  knee  posts  to  be  made  of  12"xl6"  timber  in  two  pieces,  to 
be  spliced  with  a  ship  splice  3'  long,  stringer  to  be  dressed  all  over. 
Knee  posts  to  be  framed  into  stringer  with  double  tennons;  outside 
stringer  at  end  of  knee  beams  to  be  made  of  8"xl2"  timber  in  two  pieces, 
spliced  with  ship  splices  in  center  3'  long,  *and  to  be  dressed  all  over. 

Bottom  guide  girt  to  be  made  of  12"xl6"  timber,  dressed  all  over,  one 
piece  for  each  twenty-stamp  battery,  and  to  extend  past  the  outside  posts 
12";  the  top  girt  to  be  made  of  12"xl4"  timber,  dressed  all  over,  and 
made  the  same  length  as  the  lower  ones;  all  braces  to  be  made  of  8"xl2" 
timber,  dressed  all  over,  and  framed  with  double  tennons;  no  keys  are 
to  be  used  in  braces  or  guide  girts,  but  they  must  be  accurately  fitted 
without. 

All  boxing  about  battery  frame  to  be  ■^"  deep,  and  where  braces  or 
knee  beams  are  smaller  than  the  timbers  they  frame  into,  they  must  be 
housed  in  -i"  deep;  i.  e.,  the  timber  must  not  be  boxed  out  clear  across. 

The  cam-shaft  is  to  be  set  4f"  from  the  center  to  the  center  of  the 
stems. 

A  2"  plank  floor  is  to  be  put  on  top  of  the  knee  beams,  which  is  to 
be  planed  on  the  under  side;  also,  a  2"  double  board  floor  to  be  put  in 
back  of  the  battery,  on  about  the  same  level  as  the  knee  beams. 

The  whole  Vjattery  frame  to  be  painted  with  two  coats  of  light-cream 
paint,  properly  mixed  with  oil,  and  the  wood  pulleys  and  guides  to  be 
painted  blue,  the  iron  work  to  be  painted  black.  The  out-board  bearing 
frame  to  be  made  of  12"xl6"  timber,  planed  all  over,  well  framed  and 
bolted  together,  and  anchored  to  a  solid  stone  foundation,  as  shown  in 
plan,  and  to  be  painted  same  as  battery  frame. 

Water  Wheel  Frames  are  to  be  made  of  12"xl2"  lumber  throughout, 
well  anchored  down  to  a  stone  foundation.  That  part  of  the  frame 
which  comes  above  the  floor  is  to  be  dressed  and  painted  the  same  as  the 
battery  frame. 

The  water  wheels  are  to  be  housed  with  tongued  and  grooved  lumber, 
4"  wide. 


> 


84  CALIFORNIA    GOLD    MILL    PKACTICES. 

BUILDINGS. 

Frame  Work. — Ore-house  main  frame  is  to  be  made  of  8"x8"  timbers 
throughout,  with  3"x6"  girts  and  studding. 

Battery  and  concentrator  rooms  frame  is  to  be  made  of  8"xl0"  posts 
and  chords,  6"xl0"  sills,  8"x8"  principal  rafters  and  straining  beams, 
4"x8"  truss  braces,  and  o"x6"  girts  and  studding. 

Clean-up,  sulphuret,  and  water  wheel  rooms  main  frames  are  to  be 
made  of  8"x8"  timbers,  with  3"x6"  girts  and  studding. 

Floors. — Ore-house  floors  to  be  made  of  one  thickness  of  2"  planks. 

Battery,  concentrator,  and  water  wheel  rooms  floors  are  to  made  of 
l"x8"  lumber,  double  thickness,  surfaced  on  top,  to  be  supported  on 
3"x  6"  joists  18"  apart. 

Sulphuret  and  clean-up  rooms  floors  are  to  be  made  of  concrete  laid 
on  top  of  a  heavy  wood  floor,  which  is  to  be  supported  on  foundations 
made  of  8"x  8"  timbers. 

Roofs. —  All  roofs  are  to  be  made  with  2"x8"  rafters  18"  apart,  with 
l"x6"  board  4"  apart,  and  covered  with  No.  26  standing  seam,  painted, 
iron  roofing. 

Walls. — All  walls  are  to  be  covered  with  l"x  10"  rustic. 

Cornices. — All  cornices  are  to  project  24",  measured  horizontally  from 
the  walls  of  building,  with  a  12"  frieze  and  a  5"  facia  made  of  dressed 
lumber. 

Windows. — All  windows,  except  those  for  sulphuret  room,  are  to  be 
made  of  twelve  lights  of  10"x  16"  glass,  and  frames  made  to  suit  of 
dressed  lumber,  with  casing  outside  5"  wide. 

Twelve  windows  are  to  be  put  in  the  ore-house,  seven  windows  in  the 
battery  room,  six  windows  in  the  clean-up  room,  twelve  windows  in  the 
sulphuret  room,  and  five  windows  in  the  water  wheel  room. 

Skylights. — Six  skylights,  made  of  twelve  lights  of  10"x20"  glass, 
to  be  put  into  the  roof  of  the  concentrator  room. 

Doors. — All  doors,  both  sliding  and  swinging,  to  be  3'x7'xl|"  thick, 
with  panels. 

Two  sliding  doors  are  to  be  put  in  the  ore-house,  and  one  outside 
swinging  door  in  the  battery  room;  one  swinging  door  leading  from  the 
battery  room  to  the  clean-up  room;  two  sliding  doors  leading  from  the 
concentrator  room  to  the  sulphuret  room;  two  outside  sliding  doors  for 
the  sulphuret  room,  and  one  outside  swinging  door  for  the  water  wheel 
room. 

All  doors  to  be  set  in  good  substantial  casings,  outside  cased  with 
surfaced  lumber,  and  furnished  with  all  trimmings  and  locks. 

Stairs. — There  is  to  be  a  flight  of  stairs  at  each  end  of  the  mill,  one 
flight  leading  from  the  battery  room  floor  to  the  floors  above,  and  one 
flight  of  stairs  from  the  battery  room  floor  to  the  concentrator  room  floor. 

All  stair  stringers  to  be  made  of  2"xl2"  lumber,  and  treads  of  2"x  10" 
lumber. 

Hand  Rails  are  to  be  put  on  to  the  outside  of  all  stairs  and  around 
the  landings  of  same,  also  in  front  of  the  battery  room  floor  and  all  other 
floors  and  platforms  where  there  is  danger  of  falling.  All  to  be  made 
of  dressed  lumber,  well  painted. 


CALIFORNIA    GOLD    MILL    PRACTICES.  85 

Retort  House  and  Assay  Office,  to  be  20'  wide  by  48'  long,  with  a  retort 
and  melting  furnace  room,  a  weighing  room,  and  a  storeroom;  the  two 
latter  to  be  lath  and  plaster  finished,  and  the  whole  building  to  be  fin- 
ished similar  to  the  mill  buildings,  with  iron  roof,  rustic,  etc. 

Paint  and  Whitewash. — All  buildings  are  to  be  painted  on  the  outside 
with  a  good  coat  of  brown  mineral  paint,  and  the  window  and  door 
casings  and  cornices  to  be  painted  with  two  coats  of  white  lead  paint. 

The  mill  to  be  whitewashed  throughout  the  inside,  including  the 
building  frame,  ore- bins,  etc. 

Tanks. — There  are  to  be  two  4,000-gallon  redwood  tanks,  3"  stock,  set 
up  at  the  end  of  the  mill  upon  strong  timber  foundations,  and  one  tank 
8'  wide  by  10'  long  by  4'  high,  inside  measurements,  to  be  made  of  3" 
planks,  with  8"  x  8"  frame;  planking  to  be  well  fitted  together,  and  prop- 
erly caulked  inside  with  oakum.  The  latter  tank  is  to  be  set  at  the  end 
of  the  last  sluice-box  coming  out  of  the  mill. 

•  Drain  Boxes  and  Tailings  Sluices. — Battery  sluices  and  aprons  to  be 
set  on  framework  so  arranged  that  the  grade  can  be  changed  easily. 
This  framework  to  be  planed  all  over.  Sluices  and  frames  to  be  painted 
same  as  battery  frame. 

There  will  be  a  sluice  in  front  of  battery  room  floor,  made  of  surfaced 
lumber;  also  to  be  painted  and  so  arranged  as  to  conduct  any  water 
away  which  drips  from  the  floor. 

There  will  be  sluices  put  in  under  the  concentrator  room  floor,  two  of 
which  will  be  6"  wide  by  8"  deep,  to  run  lengthwise  to  catcli  the  tailings 
from  the  concentrators,  and  one  to  be  8"  wide  by  10"  deep,  to  run  cross- 
wise and  to  take  the  tailings  from  the  first  two  sluices,  and  conduct  the 
same  outside.  All  tailings  sluices  to  have  a  fall  of  one  in  twelve,  and 
to  be  made  of  2"  lumber,  well  fitted  and  nailed  together.  Proper  sluices 
from  the  clean-up  room,  to  conduct  water  and  tailings  therefrom,  must 
be  connected  to  tailings  sluices  under  concentrator  room. 

All  sulphuret  boxes,  and  drain  boxes  for  concentrators,  to  be  made  of 
good  quality  of  redwood  lumber,  Ij"  thick,  dressed  on  both  sides,  and 
well  fitted  and  screwed  together. 

The  weight  of  all  parts  is  240,000  lbs.,  and  there  are  325,000  feet  of 
lumber  in  the  building. 

Specifications  for  a  canvas  plant  are  not  considered  necessary,  as  the 
construction  is  extremely  simple  and  no  standard  has  been  adopted. 
Full  descriptions  are  given  in  the  preceding  pages. 


I 


1 


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SEP  2  8  1978 
A. 


00  i  1  4  1983 


PHYS  SCi  LIBRARY 


p^^y,,^ 


PHYS  SCI  LIBRARY 

APR  0  3  1989 
JUN161989 
JAN  04 1990 


NOV  28  1969  IE 


RECEIVED 

NOV  29  my 


RECElfe) 


LIBRARY,  UNIVERSITY  OF  CALIFORNIA,  DAVIS 

D4613  (12/76) 


'     3  1175  00650  9478 


m 


181586 

TN 

Calif.     Dept. 

of  Natural  Resources.      Division 

?U 

of  Mines. 

C3 

Bulletin. 

A3 

no.  6 

197^ 

PHYSICAL 

SCIENCES 

'  iRPaRY 

• 

i'/ 


PS 
L 


